diff --git a/caffeine/build.gradle.kts b/caffeine/build.gradle.kts
index 33c99a2d34..0fe16e2c77 100644
--- a/caffeine/build.gradle.kts
+++ b/caffeine/build.gradle.kts
@@ -29,7 +29,7 @@ val javaPoetRuntimeOnly: Configuration = configurations["javaPoetRuntimeOnly"]
 val javaPoetImplementation: Configuration = configurations["javaPoetImplementation"]
 
 dependencies {
-  api(libs.checker.annotations)
+  api(libs.jspecify)
   api(libs.errorprone.annotations)
 
   testImplementation(libs.joor)
@@ -75,6 +75,7 @@ dependencies {
 
   javaPoetImplementation(libs.guava)
   javaPoetImplementation(libs.javapoet)
+  javaPoetImplementation(libs.jspecify)
   javaPoetImplementation(libs.commons.lang3)
 
   javaPoetRuntimeOnly(libs.google.java.format)
diff --git a/caffeine/src/javaPoet/java/com/github/benmanes/caffeine/cache/Specifications.java b/caffeine/src/javaPoet/java/com/github/benmanes/caffeine/cache/Specifications.java
index 3c770e0932..8305fbf5dd 100644
--- a/caffeine/src/javaPoet/java/com/github/benmanes/caffeine/cache/Specifications.java
+++ b/caffeine/src/javaPoet/java/com/github/benmanes/caffeine/cache/Specifications.java
@@ -20,7 +20,7 @@
 import java.lang.ref.Reference;
 import java.lang.ref.ReferenceQueue;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.squareup.javapoet.ClassName;
 import com.squareup.javapoet.ParameterSpec;
diff --git a/caffeine/src/javaPoet/java/com/github/benmanes/caffeine/cache/local/package-info.java b/caffeine/src/javaPoet/java/com/github/benmanes/caffeine/cache/local/package-info.java
index 5c5a45b927..f651d881b1 100644
--- a/caffeine/src/javaPoet/java/com/github/benmanes/caffeine/cache/local/package-info.java
+++ b/caffeine/src/javaPoet/java/com/github/benmanes/caffeine/cache/local/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.local;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/caffeine/src/javaPoet/java/com/github/benmanes/caffeine/cache/node/package-info.java b/caffeine/src/javaPoet/java/com/github/benmanes/caffeine/cache/node/package-info.java
index f20678411b..dfe66c8b7a 100644
--- a/caffeine/src/javaPoet/java/com/github/benmanes/caffeine/cache/node/package-info.java
+++ b/caffeine/src/javaPoet/java/com/github/benmanes/caffeine/cache/node/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.node;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/caffeine/src/javaPoet/java/com/github/benmanes/caffeine/cache/package-info.java b/caffeine/src/javaPoet/java/com/github/benmanes/caffeine/cache/package-info.java
index 6a536374b0..a00ec4f1f7 100644
--- a/caffeine/src/javaPoet/java/com/github/benmanes/caffeine/cache/package-info.java
+++ b/caffeine/src/javaPoet/java/com/github/benmanes/caffeine/cache/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/caffeine/src/jmh/java/com/github/benmanes/caffeine/DelegationBenchmark.java b/caffeine/src/jmh/java/com/github/benmanes/caffeine/DelegationBenchmark.java
index 15dc7d81e1..de30af8889 100644
--- a/caffeine/src/jmh/java/com/github/benmanes/caffeine/DelegationBenchmark.java
+++ b/caffeine/src/jmh/java/com/github/benmanes/caffeine/DelegationBenchmark.java
@@ -19,7 +19,7 @@
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ThreadLocalRandom;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 import org.openjdk.jmh.annotations.Benchmark;
 import org.openjdk.jmh.annotations.Scope;
 import org.openjdk.jmh.annotations.Setup;
diff --git a/caffeine/src/jmh/java/com/github/benmanes/caffeine/cache/BasicCache.java b/caffeine/src/jmh/java/com/github/benmanes/caffeine/cache/BasicCache.java
index d65f20dcc8..5418d88343 100644
--- a/caffeine/src/jmh/java/com/github/benmanes/caffeine/cache/BasicCache.java
+++ b/caffeine/src/jmh/java/com/github/benmanes/caffeine/cache/BasicCache.java
@@ -15,7 +15,7 @@
  */
 package com.github.benmanes.caffeine.cache;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 /**
  * A facade for benchmark implementations.
diff --git a/caffeine/src/jmh/java/com/github/benmanes/caffeine/cache/TimerWheelBenchmark.java b/caffeine/src/jmh/java/com/github/benmanes/caffeine/cache/TimerWheelBenchmark.java
index 209e1f71b2..aa113f23fa 100644
--- a/caffeine/src/jmh/java/com/github/benmanes/caffeine/cache/TimerWheelBenchmark.java
+++ b/caffeine/src/jmh/java/com/github/benmanes/caffeine/cache/TimerWheelBenchmark.java
@@ -19,7 +19,7 @@
 import java.util.concurrent.ThreadLocalRandom;
 import java.util.concurrent.TimeUnit;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 import org.openjdk.jmh.annotations.Benchmark;
 import org.openjdk.jmh.annotations.Scope;
 import org.openjdk.jmh.annotations.Setup;
diff --git a/caffeine/src/jmh/java/com/github/benmanes/caffeine/cache/impl/package-info.java b/caffeine/src/jmh/java/com/github/benmanes/caffeine/cache/impl/package-info.java
index 763f9fa0c5..440483b94d 100644
--- a/caffeine/src/jmh/java/com/github/benmanes/caffeine/cache/impl/package-info.java
+++ b/caffeine/src/jmh/java/com/github/benmanes/caffeine/cache/impl/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.impl;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/caffeine/src/jmh/java/com/github/benmanes/caffeine/cache/package-info.java b/caffeine/src/jmh/java/com/github/benmanes/caffeine/cache/package-info.java
index 6a536374b0..a00ec4f1f7 100644
--- a/caffeine/src/jmh/java/com/github/benmanes/caffeine/cache/package-info.java
+++ b/caffeine/src/jmh/java/com/github/benmanes/caffeine/cache/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/caffeine/src/jmh/java/com/github/benmanes/caffeine/cache/sketch/CountMinSketch.java b/caffeine/src/jmh/java/com/github/benmanes/caffeine/cache/sketch/CountMinSketch.java
index 49db9d33c8..c62f8f731d 100644
--- a/caffeine/src/jmh/java/com/github/benmanes/caffeine/cache/sketch/CountMinSketch.java
+++ b/caffeine/src/jmh/java/com/github/benmanes/caffeine/cache/sketch/CountMinSketch.java
@@ -17,8 +17,6 @@
 
 import static com.google.common.base.Preconditions.checkArgument;
 
-import org.checkerframework.checker.index.qual.NonNegative;
-
 import com.google.common.math.IntMath;
 
 /**
@@ -77,7 +75,7 @@ public CountMinSketch() {}
    *
    * @param maximumSize the maximum size of the cache
    */
-  public void ensureCapacity(@NonNegative long maximumSize) {
+  public void ensureCapacity(long maximumSize) {
     checkArgument(maximumSize >= 0);
     int maximum = (int) Math.min(maximumSize, Integer.MAX_VALUE >>> 1);
     if ((table != null) && (table.length >= maximum)) {
@@ -107,7 +105,7 @@ public boolean isNotInitialized() {
    * @param e the element to count occurrences of
    * @return the estimated number of occurrences of the element; possibly zero but never negative
    */
-  public @NonNegative int frequency(E e) {
+  public int frequency(E e) {
     if (isNotInitialized()) {
       return 0;
     }
diff --git a/caffeine/src/jmh/java/com/github/benmanes/caffeine/cache/sketch/package-info.java b/caffeine/src/jmh/java/com/github/benmanes/caffeine/cache/sketch/package-info.java
index 0f23542b7b..bb53977942 100644
--- a/caffeine/src/jmh/java/com/github/benmanes/caffeine/cache/sketch/package-info.java
+++ b/caffeine/src/jmh/java/com/github/benmanes/caffeine/cache/sketch/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.sketch;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/caffeine/src/jmh/java/com/github/benmanes/caffeine/package-info.java b/caffeine/src/jmh/java/com/github/benmanes/caffeine/package-info.java
index 7e490e3225..3339cf3563 100644
--- a/caffeine/src/jmh/java/com/github/benmanes/caffeine/package-info.java
+++ b/caffeine/src/jmh/java/com/github/benmanes/caffeine/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/caffeine/src/jmh/java/com/github/benmanes/caffeine/profiler/package-info.java b/caffeine/src/jmh/java/com/github/benmanes/caffeine/profiler/package-info.java
index 10dffd255c..aafe8e615e 100644
--- a/caffeine/src/jmh/java/com/github/benmanes/caffeine/profiler/package-info.java
+++ b/caffeine/src/jmh/java/com/github/benmanes/caffeine/profiler/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.profiler;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/AbstractLinkedDeque.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/AbstractLinkedDeque.java
index ee2b250633..ee29d30648 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/AbstractLinkedDeque.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/AbstractLinkedDeque.java
@@ -20,7 +20,7 @@
 import java.util.ConcurrentModificationException;
 import java.util.NoSuchElementException;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.google.errorprone.annotations.Var;
 
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/AccessOrderDeque.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/AccessOrderDeque.java
index 45c5b72eb1..93d34a6faf 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/AccessOrderDeque.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/AccessOrderDeque.java
@@ -17,7 +17,7 @@
 
 import java.util.Deque;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.AccessOrderDeque.AccessOrder;
 
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Async.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Async.java
index c4f7e81aee..331d588e78 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Async.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Async.java
@@ -26,7 +26,7 @@
 import java.util.concurrent.CompletionException;
 import java.util.concurrent.Executor;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Static utility methods and classes pertaining to asynchronous operations.
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/AsyncCache.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/AsyncCache.java
index 6fd3e1174d..a7e5d37af0 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/AsyncCache.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/AsyncCache.java
@@ -23,7 +23,8 @@
 import java.util.function.BiFunction;
 import java.util.function.Function;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.NullMarked;
+import org.jspecify.annotations.Nullable;
 
 /**
  * A semi-persistent mapping from keys to values. Cache entries are manually added using
@@ -37,6 +38,7 @@
  * @param <K> the type of keys maintained by this cache
  * @param <V> the type of mapped values
  */
+@NullMarked
 public interface AsyncCache<K, V> {
 
   /**
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/AsyncCacheLoader.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/AsyncCacheLoader.java
index b2c0948611..745922807a 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/AsyncCacheLoader.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/AsyncCacheLoader.java
@@ -24,6 +24,8 @@
 import java.util.function.BiFunction;
 import java.util.function.Function;
 
+import org.jspecify.annotations.NullMarked;
+
 /**
  * Computes or retrieves values asynchronously based on a key, for use in populating a
  * {@link AsyncLoadingCache}.
@@ -42,6 +44,7 @@
  * @param <V> the type of values
  * @author ben.manes@gmail.com (Ben Manes)
  */
+@NullMarked
 @FunctionalInterface
 @SuppressWarnings("PMD.SignatureDeclareThrowsException")
 public interface AsyncCacheLoader<K, V> {
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/AsyncLoadingCache.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/AsyncLoadingCache.java
index ee1eb9357c..8b60c3168d 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/AsyncLoadingCache.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/AsyncLoadingCache.java
@@ -18,6 +18,8 @@
 import java.util.Map;
 import java.util.concurrent.CompletableFuture;
 
+import org.jspecify.annotations.NullMarked;
+
 /**
  * A semi-persistent mapping from keys to values. Values are automatically loaded by the cache
  * asynchronously and are stored in the cache until either evicted or manually invalidated.
@@ -29,6 +31,7 @@
  * @param <K> the type of keys maintained by this cache
  * @param <V> the type of mapped values
  */
+@NullMarked
 public interface AsyncLoadingCache<K, V> extends AsyncCache<K, V> {
 
   /**
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/BoundedLocalCache.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/BoundedLocalCache.java
index a1e5129148..a588512dd9 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/BoundedLocalCache.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/BoundedLocalCache.java
@@ -83,7 +83,7 @@
 import java.util.stream.Stream;
 import java.util.stream.StreamSupport;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.Async.AsyncExpiry;
 import com.github.benmanes.caffeine.cache.LinkedDeque.PeekingIterator;
@@ -3011,7 +3011,7 @@ public Set<Entry<K, V>> entrySet() {
    * {@link #size()} as many usages assume it to be instantaneous and lock-free.
    */
   @Override
-  public boolean equals(Object o) {
+  public boolean equals(@Nullable Object o) {
     if (o == this) {
       return true;
     } else if (!(o instanceof Map)) {
@@ -3090,7 +3090,7 @@ public String toString() {
    * @return the computed value
    */
   @SuppressWarnings("GuardedByChecker")
-  <T> T evictionOrder(boolean hottest, Function<V, V> transformer,
+  <T> T evictionOrder(boolean hottest, Function<@Nullable V, @Nullable V> transformer,
       Function<Stream<CacheEntry<K, V>>, T> mappingFunction) {
     Comparator<Node<K, V>> comparator = Comparator.comparingInt(node -> {
       K key = node.getKey();
@@ -3125,7 +3125,7 @@ <T> T evictionOrder(boolean hottest, Function<V, V> transformer,
    * @return the computed value
    */
   @SuppressWarnings("GuardedByChecker")
-  <T> T expireAfterAccessOrder(boolean oldest, Function<V, V> transformer,
+  <T> T expireAfterAccessOrder(boolean oldest, Function<@Nullable V, @Nullable V> transformer,
       Function<Stream<CacheEntry<K, V>>, T> mappingFunction) {
     Iterable<Node<K, V>> iterable;
     if (evicts()) {
@@ -3163,7 +3163,7 @@ <T> T expireAfterAccessOrder(boolean oldest, Function<V, V> transformer,
    * @param mappingFunction the mapping function to compute a value
    * @return the computed value
    */
-  <T> T snapshot(Iterable<Node<K, V>> iterable, Function<V, V> transformer,
+  <T> T snapshot(Iterable<Node<K, V>> iterable, Function<@Nullable V, @Nullable V> transformer,
       Function<Stream<CacheEntry<K, V>>, T> mappingFunction) {
     requireNonNull(mappingFunction);
     requireNonNull(transformer);
@@ -3865,7 +3865,7 @@ public int characteristics() {
   }
 
   /** A reusable task that performs the maintenance work; used to avoid wrapping by ForkJoinPool. */
-  static final class PerformCleanupTask extends ForkJoinTask<Void> implements Runnable {
+  static final class PerformCleanupTask extends ForkJoinTask<@Nullable Void> implements Runnable {
     private static final long serialVersionUID = 1L;
 
     final WeakReference<BoundedLocalCache<?, ?>> reference;
@@ -3901,10 +3901,10 @@ public void run() {
      */
     // public final void quietlyComplete() {}
 
-    @Override public Void getRawResult() { return null; }
-    @Override public void setRawResult(Void v) {}
-    @Override public void complete(Void value) {}
+    @Override public void setRawResult(@Nullable Void v) {}
+    @Override public void complete(@Nullable Void value) {}
     @Override public void completeExceptionally(Throwable ex) {}
+    @Override public @Nullable Void getRawResult() { return null; }
     @Override public boolean cancel(boolean mayInterruptIfRunning) { return false; }
   }
 
@@ -3967,8 +3967,12 @@ public BoundedLocalCache<K, V> cache() {
 
     @Override
     public Policy<K, V> policy() {
-      var p = policy;
-      return (p == null) ? (policy = new BoundedPolicy<>(cache, identity(), cache.isWeighted)) : p;
+      if (policy == null) {
+        @SuppressWarnings("NullAway")
+        Function<@Nullable V, @Nullable V> identity = identity();
+        policy = new BoundedPolicy<>(cache, identity, cache.isWeighted);
+      }
+      return policy;
     }
 
     private void readObject(ObjectInputStream stream) throws InvalidObjectException {
@@ -4527,8 +4531,8 @@ public Policy<K, V> policy() {
         @SuppressWarnings("unchecked")
         var castCache = (BoundedLocalCache<K, V>) cache;
         Function<CompletableFuture<V>, @Nullable V> transformer = Async::getIfReady;
-        @SuppressWarnings("unchecked")
-        var castTransformer = (Function<V, V>) transformer;
+        @SuppressWarnings({"NullAway", "unchecked", "Varifier"})
+        Function<@Nullable V, @Nullable V> castTransformer = (Function<V, V>) transformer;
         policy = new BoundedPolicy<>(castCache, castTransformer, isWeighted);
       }
       return policy;
@@ -4579,8 +4583,8 @@ public Policy<K, V> policy() {
         @SuppressWarnings("unchecked")
         var castCache = (BoundedLocalCache<K, V>) cache;
         Function<CompletableFuture<V>, @Nullable V> transformer = Async::getIfReady;
-        @SuppressWarnings("unchecked")
-        var castTransformer = (Function<V, V>) transformer;
+        @SuppressWarnings({"NullAway", "unchecked", "Varifier"})
+        Function<@Nullable V, @Nullable V> castTransformer = (Function<V, V>) transformer;
         policy = new BoundedPolicy<>(castCache, castTransformer, isWeighted);
       }
       return policy;
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Cache.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Cache.java
index 251e4c8a46..cddcd68179 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Cache.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Cache.java
@@ -20,9 +20,8 @@
 import java.util.concurrent.ConcurrentMap;
 import java.util.function.Function;
 
-import org.checkerframework.checker.index.qual.NonNegative;
-import org.checkerframework.checker.nullness.qual.Nullable;
-import org.checkerframework.checker.nullness.qual.PolyNull;
+import org.jspecify.annotations.NullMarked;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.stats.CacheStats;
 
@@ -38,6 +37,7 @@
  * @param <K> the type of keys maintained by this cache
  * @param <V> the type of mapped values
  */
+@NullMarked
 public interface Cache<K, V> {
 
   /**
@@ -77,8 +77,7 @@ public interface Cache<K, V> {
    * @throws RuntimeException or Error if the mappingFunction does so, in which case the mapping is
    *         left unestablished
    */
-  @PolyNull
-  V get(K key, Function<? super K, ? extends @PolyNull V> mappingFunction);
+  V get(K key, Function<? super K, ? extends V> mappingFunction);
 
   /**
    * Returns a map of the values associated with the {@code keys} in this cache. The returned map
@@ -180,7 +179,6 @@ Map<K, V> getAll(Iterable<? extends K> keys,
    *
    * @return the estimated number of mappings
    */
-  @NonNegative
   long estimatedSize();
 
   /**
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/CacheLoader.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/CacheLoader.java
index 84e842fa6a..217c81a868 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/CacheLoader.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/CacheLoader.java
@@ -24,7 +24,8 @@
 import java.util.concurrent.Executor;
 import java.util.function.Function;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.NullMarked;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Computes or retrieves values, based on a key, for use in populating a {@link LoadingCache} or
@@ -43,6 +44,7 @@
  * @param <V> the type of values
  * @author ben.manes@gmail.com (Ben Manes)
  */
+@NullMarked
 @FunctionalInterface
 @SuppressWarnings({"FunctionalInterfaceMethodChanged", "PMD.SignatureDeclareThrowsException"})
 public interface CacheLoader<K, V> extends AsyncCacheLoader<K, V> {
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Caffeine.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Caffeine.java
index 12296fc8db..f4e5f23428 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Caffeine.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Caffeine.java
@@ -36,8 +36,8 @@
 import java.util.concurrent.TimeUnit;
 import java.util.function.Supplier;
 
-import org.checkerframework.checker.index.qual.NonNegative;
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.NullMarked;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.Async.AsyncEvictionListener;
 import com.github.benmanes.caffeine.cache.Async.AsyncExpiry;
@@ -137,6 +137,7 @@
  *     normally {@code Object} unless it is constrained by using a method like {@code
  *     #removalListener}
  */
+@NullMarked
 public final class Caffeine<K, V> {
   static final Supplier<StatsCounter> ENABLED_STATS_COUNTER_SUPPLIER = ConcurrentStatsCounter::new;
   static final Logger logger = System.getLogger(Caffeine.class.getName());
@@ -309,7 +310,7 @@ public static Caffeine<Object, Object> from(String spec) {
    * @throws IllegalStateException if an initial capacity was already set
    */
   @CanIgnoreReturnValue
-  public Caffeine<K, V> initialCapacity(@NonNegative int initialCapacity) {
+  public Caffeine<K, V> initialCapacity(int initialCapacity) {
     requireState(this.initialCapacity == UNSET_INT,
         "initial capacity was already set to %s", this.initialCapacity);
     requireArgument(initialCapacity >= 0);
@@ -407,7 +408,7 @@ Scheduler getScheduler() {
    * @throws IllegalStateException if a maximum size or weight was already set
    */
   @CanIgnoreReturnValue
-  public Caffeine<K, V> maximumSize(@NonNegative long maximumSize) {
+  public Caffeine<K, V> maximumSize(long maximumSize) {
     requireState(this.maximumSize == UNSET_INT,
         "maximum size was already set to %s", this.maximumSize);
     requireState(this.maximumWeight == UNSET_INT,
@@ -444,7 +445,7 @@ public Caffeine<K, V> maximumSize(@NonNegative long maximumSize) {
    * @throws IllegalStateException if a maximum weight or size was already set
    */
   @CanIgnoreReturnValue
-  public Caffeine<K, V> maximumWeight(@NonNegative long maximumWeight) {
+  public Caffeine<K, V> maximumWeight(long maximumWeight) {
     requireState(this.maximumWeight == UNSET_INT,
         "maximum weight was already set to %s", this.maximumWeight);
     requireState(this.maximumSize == UNSET_INT,
@@ -652,7 +653,7 @@ public Caffeine<K, V> expireAfterWrite(Duration duration) {
    * @throws IllegalStateException if the time to live or variable expiration was already set
    */
   @CanIgnoreReturnValue
-  public Caffeine<K, V> expireAfterWrite(@NonNegative long duration, TimeUnit unit) {
+  public Caffeine<K, V> expireAfterWrite(long duration, TimeUnit unit) {
     requireState(expireAfterWriteNanos == UNSET_INT,
         "expireAfterWrite was already set to %s ns", expireAfterWriteNanos);
     requireState(expiry == null, "expireAfterWrite may not be used with variable expiration");
@@ -716,7 +717,7 @@ public Caffeine<K, V> expireAfterAccess(Duration duration) {
    * @throws IllegalStateException if the time to idle or variable expiration was already set
    */
   @CanIgnoreReturnValue
-  public Caffeine<K, V> expireAfterAccess(@NonNegative long duration, TimeUnit unit) {
+  public Caffeine<K, V> expireAfterAccess(long duration, TimeUnit unit) {
     requireState(expireAfterAccessNanos == UNSET_INT,
         "expireAfterAccess was already set to %s ns", expireAfterAccessNanos);
     requireState(expiry == null, "expireAfterAccess may not be used with variable expiration");
@@ -836,7 +837,7 @@ public Caffeine<K, V> refreshAfterWrite(Duration duration) {
    * @throws IllegalStateException if the refresh interval was already set
    */
   @CanIgnoreReturnValue
-  public Caffeine<K, V> refreshAfterWrite(@NonNegative long duration, TimeUnit unit) {
+  public Caffeine<K, V> refreshAfterWrite(long duration, TimeUnit unit) {
     requireNonNull(unit);
     requireState(refreshAfterWriteNanos == UNSET_INT,
         "refreshAfterWriteNanos was already set to %s ns", refreshAfterWriteNanos);
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/CaffeineSpec.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/CaffeineSpec.java
index a920c16953..fb67357a1f 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/CaffeineSpec.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/CaffeineSpec.java
@@ -25,7 +25,8 @@
 import java.util.Objects;
 import java.util.concurrent.TimeUnit;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.NullMarked;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.Caffeine.Strength;
 
@@ -70,6 +71,7 @@
  *
  * @author ben.manes@gmail.com (Ben Manes)
  */
+@NullMarked
 public final class CaffeineSpec {
   static final String SPLIT_OPTIONS = ",";
   static final String SPLIT_KEY_VALUE = "=";
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Expiry.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Expiry.java
index bdeaccd87a..15a04ede98 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Expiry.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Expiry.java
@@ -22,7 +22,7 @@
 import java.time.Duration;
 import java.util.function.BiFunction;
 
-import org.checkerframework.checker.index.qual.NonNegative;
+import org.jspecify.annotations.NullMarked;
 
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
 
@@ -42,6 +42,7 @@
  * @param <V> the type of values
  * @author ben.manes@gmail.com (Ben Manes)
  */
+@NullMarked
 public interface Expiry<K, V> {
 
   /**
@@ -76,7 +77,7 @@ public interface Expiry<K, V> {
    * @param currentDuration the entry's current duration, in nanoseconds
    * @return the length of time before the entry expires, in nanoseconds
    */
-  long expireAfterUpdate(K key, V value, long currentTime, @NonNegative long currentDuration);
+  long expireAfterUpdate(K key, V value, long currentTime, long currentDuration);
 
   /**
    * Specifies that the entry should be automatically removed from the cache once the duration has
@@ -94,7 +95,7 @@ public interface Expiry<K, V> {
    * @param currentDuration the entry's current duration, in nanoseconds
    * @return the length of time before the entry expires, in nanoseconds
    */
-  long expireAfterRead(K key, V value, long currentTime, @NonNegative long currentDuration);
+  long expireAfterRead(K key, V value, long currentTime, long currentDuration);
 
   /**
    * Returns an {@code Expiry} that specifies that the entry should be automatically removed from
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/FrequencySketch.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/FrequencySketch.java
index d3a40e893a..fc319e512c 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/FrequencySketch.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/FrequencySketch.java
@@ -17,8 +17,6 @@
 
 import static com.github.benmanes.caffeine.cache.Caffeine.requireArgument;
 
-import org.checkerframework.checker.index.qual.NonNegative;
-
 import com.google.errorprone.annotations.Var;
 
 /**
@@ -88,7 +86,7 @@ public FrequencySketch() {}
    * @param maximumSize the maximum size of the cache
    */
   @SuppressWarnings("Varifier")
-  public void ensureCapacity(@NonNegative long maximumSize) {
+  public void ensureCapacity(long maximumSize) {
     requireArgument(maximumSize >= 0);
     int maximum = (int) Math.min(maximumSize, Integer.MAX_VALUE >>> 1);
     if ((table != null) && (table.length >= maximum)) {
@@ -119,7 +117,7 @@ public boolean isNotInitialized() {
    * @return the estimated number of occurrences of the element; possibly zero but never negative
    */
   @SuppressWarnings("Varifier")
-  public @NonNegative int frequency(E e) {
+  public int frequency(E e) {
     if (isNotInitialized()) {
       return 0;
     }
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Interner.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Interner.java
index f995c60ccb..c6210dc276 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Interner.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Interner.java
@@ -21,6 +21,8 @@
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentMap;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.github.benmanes.caffeine.cache.References.LookupKeyEqualsReference;
 import com.github.benmanes.caffeine.cache.References.WeakKeyEqualsReference;
 
@@ -34,6 +36,7 @@
  * @param <E> the type of elements
  * @author ben.manes@gmail.com (Ben Manes)
  */
+@NullMarked
 @FunctionalInterface
 public interface Interner<E> {
 
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LinkedDeque.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LinkedDeque.java
index 44a311d1fe..9c3fed30df 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LinkedDeque.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LinkedDeque.java
@@ -21,7 +21,7 @@
 import java.util.Iterator;
 import java.util.NoSuchElementException;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 /**
  * A linked list extension of the {@link Deque} interface where the link pointers are tightly
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LoadingCache.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LoadingCache.java
index 564c13c2c2..c06aeb2116 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LoadingCache.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LoadingCache.java
@@ -19,6 +19,8 @@
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.CompletionException;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
 
 /**
@@ -32,6 +34,7 @@
  * @param <K> the type of keys maintained by this cache
  * @param <V> the type of mapped values
  */
+@NullMarked
 public interface LoadingCache<K, V> extends Cache<K, V> {
 
   /**
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LocalAsyncCache.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LocalAsyncCache.java
index 5170ac155f..fa2e56b7df 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LocalAsyncCache.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LocalAsyncCache.java
@@ -44,7 +44,7 @@
 import java.util.function.Function;
 import java.util.function.Predicate;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.LocalAsyncCache.AsyncBulkCompleter.NullMapCompletionException;
 import com.github.benmanes.caffeine.cache.stats.CacheStats;
@@ -500,7 +500,7 @@ public boolean replace(K key, CompletableFuture<V> oldValue, CompletableFuture<V
       return asyncCache.cache().entrySet();
     }
     @SuppressWarnings("EqualsWhichDoesntCheckParameterClass")
-    @Override public boolean equals(Object o) {
+    @Override public boolean equals(@Nullable Object o) {
       return asyncCache.cache().equals(o);
     }
     @Override public int hashCode() {
@@ -1022,7 +1022,7 @@ public Set<Entry<K, V>> entrySet() {
 
     /** See {@link BoundedLocalCache#equals(Object)} for semantics. */
     @Override
-    public boolean equals(Object o) {
+    public boolean equals(@Nullable Object o) {
       if (o == this) {
         return true;
       } else if (!(o instanceof Map)) {
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LocalAsyncLoadingCache.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LocalAsyncLoadingCache.java
index fd406d3c4b..0452622871 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LocalAsyncLoadingCache.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LocalAsyncLoadingCache.java
@@ -33,7 +33,7 @@
 import java.util.function.BiFunction;
 import java.util.function.Function;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.google.errorprone.annotations.Var;
 
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LocalCache.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LocalCache.java
index 0024e52edd..c3dc388a31 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LocalCache.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LocalCache.java
@@ -22,7 +22,7 @@
 import java.util.function.BiFunction;
 import java.util.function.Function;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.stats.StatsCounter;
 
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LocalCacheFactory.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LocalCacheFactory.java
index b1295ccc52..6229a1e161 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LocalCacheFactory.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LocalCacheFactory.java
@@ -21,7 +21,7 @@
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentMap;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.google.errorprone.annotations.Var;
 
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LocalLoadingCache.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LocalLoadingCache.java
index 0765da35b7..1fb618c693 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LocalLoadingCache.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LocalLoadingCache.java
@@ -32,7 +32,7 @@
 import java.util.concurrent.TimeoutException;
 import java.util.function.Function;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.google.errorprone.annotations.Var;
 
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LocalManualCache.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LocalManualCache.java
index f57a35d238..d2e008b2f5 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LocalManualCache.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/LocalManualCache.java
@@ -26,7 +26,7 @@
 import java.util.concurrent.ConcurrentMap;
 import java.util.function.Function;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.stats.CacheStats;
 import com.google.errorprone.annotations.Var;
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Node.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Node.java
index 3304ce4b44..d5135afc81 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Node.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Node.java
@@ -19,8 +19,7 @@
 
 import java.lang.ref.ReferenceQueue;
 
-import org.checkerframework.checker.index.qual.NonNegative;
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.AccessOrderDeque.AccessOrder;
 import com.github.benmanes.caffeine.cache.WriteOrderDeque.WriteOrder;
@@ -64,23 +63,23 @@ abstract class Node<K, V> implements AccessOrder<Node<K, V>>, WriteOrder<Node<K,
 
   /** Returns the weight of this entry from the entry's perspective. */
   @GuardedBy("this")
-  public @NonNegative int getWeight() {
+  public int getWeight() {
     return 1;
   }
 
   /** Sets the weight from the entry's perspective. */
   @GuardedBy("this")
-  public void setWeight(@NonNegative int weight) {}
+  public void setWeight(int weight) {}
 
   /** Returns the weight of this entry from the policy's perspective. */
   // @GuardedBy("evictionLock")
-  public @NonNegative int getPolicyWeight() {
+  public int getPolicyWeight() {
     return 1;
   }
 
   /** Sets the weight from the policy's perspective. */
   // @GuardedBy("evictionLock")
-  public void setPolicyWeight(@NonNegative int weight) {}
+  public void setPolicyWeight(int weight) {}
 
   /* --------------- Health --------------- */
 
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Pacer.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Pacer.java
index b572e5b8c1..32a42d13ea 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Pacer.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Pacer.java
@@ -22,7 +22,7 @@
 import java.util.concurrent.Future;
 import java.util.concurrent.TimeUnit;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 /**
  * A pacing scheduler that prevents executions from happening too frequently. Only one task may be
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Policy.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Policy.java
index 7cc115da99..a8f77da481 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Policy.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Policy.java
@@ -29,9 +29,8 @@
 import java.util.function.Function;
 import java.util.stream.Stream;
 
-import org.checkerframework.checker.index.qual.NonNegative;
-import org.checkerframework.checker.nullness.qual.Nullable;
-import org.checkerframework.checker.nullness.qual.PolyNull;
+import org.jspecify.annotations.NullMarked;
+import org.jspecify.annotations.Nullable;
 
 /**
  * An access point for inspecting and performing low-level operations based on the cache's runtime
@@ -42,6 +41,7 @@
  * @param <V> the type of values
  * @author ben.manes@gmail.com (Ben Manes)
  */
+@NullMarked
 public interface Policy<K, V> {
 
   /**
@@ -189,7 +189,6 @@ interface Eviction<K, V> {
      *
      * @return the maximum size bounding, which may be either weighted or unweighted
      */
-    @NonNegative
     long getMaximum();
 
     /**
@@ -205,7 +204,7 @@ interface Eviction<K, V> {
      *        cache was constructed
      * @throws IllegalArgumentException if the maximum size specified is negative
      */
-    void setMaximum(@NonNegative long maximum);
+    void setMaximum(long maximum);
 
     /**
      * Returns an unmodifiable snapshot {@link Map} view of the cache with ordered traversal. The
@@ -220,8 +219,9 @@ interface Eviction<K, V> {
      * @param limit the maximum size of the returned map (use {@link Integer#MAX_VALUE} to disregard
      *        the limit)
      * @return a snapshot view of the cache from the coldest entry to the hottest
+     * @throws IllegalArgumentException if the limit specified is negative
      */
-    Map<K, V> coldest(@NonNegative int limit);
+    Map<K, V> coldest(int limit);
 
     /**
      * Returns an unmodifiable snapshot {@link Map} view of the cache with ordered traversal. The
@@ -237,8 +237,9 @@ interface Eviction<K, V> {
      * @param weightLimit the maximum weight of the returned map (use {@link Long#MAX_VALUE} to
      *        disregard the limit)
      * @return a snapshot view of the cache from the coldest entry to the hottest
+     * @throws IllegalArgumentException if the limit specified is negative
      */
-    default Map<K, V> coldestWeighted(@NonNegative long weightLimit) {
+    default Map<K, V> coldestWeighted(long weightLimit) {
       // This method was added & implemented in version 3.0.4
       throw new UnsupportedOperationException();
     }
@@ -285,8 +286,9 @@ default <T> T coldest(Function<Stream<CacheEntry<K, V>>, T> mappingFunction) {
      * @param limit the maximum size of the returned map (use {@link Integer#MAX_VALUE} to disregard
      *        the limit)
      * @return a snapshot view of the cache from the hottest entry to the coldest
+     * @throws IllegalArgumentException if the limit specified is negative
      */
-    Map<K, V> hottest(@NonNegative int limit);
+    Map<K, V> hottest(int limit);
 
     /**
      * Returns an unmodifiable snapshot {@link Map} view of the cache with ordered traversal. The
@@ -302,8 +304,9 @@ default <T> T coldest(Function<Stream<CacheEntry<K, V>>, T> mappingFunction) {
      * @param weightLimit the maximum weight of the returned map (use {@link Long#MAX_VALUE} to
      *        disregard the limit)
      * @return a snapshot view of the cache from the hottest entry to the coldest
+     * @throws IllegalArgumentException if the limit specified is negative
      */
-    default Map<K, V> hottestWeighted(@NonNegative long weightLimit) {
+    default Map<K, V> hottestWeighted(long weightLimit) {
       // This method was added & implemented in version 3.0.4
       throw new UnsupportedOperationException();
     }
@@ -390,7 +393,6 @@ default Optional<Duration> ageOf(K key) {
      * @return the length of time after which an entry should be automatically removed
      * @throws NullPointerException if the unit is null
      */
-    @NonNegative
     long getExpiresAfter(TimeUnit unit);
 
     /**
@@ -414,7 +416,7 @@ default Duration getExpiresAfter() {
      * @throws IllegalArgumentException if {@code duration} is negative
      * @throws NullPointerException if the unit is null
      */
-    void setExpiresAfter(@NonNegative long duration, TimeUnit unit);
+    void setExpiresAfter(long duration, TimeUnit unit);
 
     /**
      * Specifies that each entry should be automatically removed from the cache once a fixed
@@ -441,8 +443,9 @@ default void setExpiresAfter(Duration duration) {
      * @param limit the maximum size of the returned map (use {@link Integer#MAX_VALUE} to disregard
      *        the limit)
      * @return a snapshot view of the cache from the oldest entry to the youngest
+     * @throws IllegalArgumentException if the limit specified is negative
      */
-    Map<K, V> oldest(@NonNegative int limit);
+    Map<K, V> oldest(int limit);
 
     /**
      * Returns the computed result from the ordered traversal of the cache entries. The oorder of
@@ -484,8 +487,9 @@ default <T> T oldest(Function<Stream<CacheEntry<K, V>>, T> mappingFunction) {
      * @param limit the maximum size of the returned map (use {@link Integer#MAX_VALUE} to disregard
      *        the limit)
      * @return a snapshot view of the cache from the youngest entry to the oldest
+     * @throws IllegalArgumentException if the limit specified is negative
      */
-    Map<K, V> youngest(@NonNegative int limit);
+    Map<K, V> youngest(int limit);
 
     /**
      * Returns the computed result from the ordered traversal of the cache entries. The order of
@@ -559,7 +563,7 @@ default Optional<Duration> getExpiresAfter(K key) {
      * @throws IllegalArgumentException if {@code duration} is negative
      * @throws NullPointerException if the specified key or unit is null
      */
-    void setExpiresAfter(K key, @NonNegative long duration, TimeUnit unit);
+    void setExpiresAfter(K key, long duration, TimeUnit unit);
 
     /**
      * Specifies that the entry should be automatically removed from the cache once the duration has
@@ -589,7 +593,7 @@ default void setExpiresAfter(K key, Duration duration) {
      * @throws IllegalArgumentException if {@code duration} is negative
      * @throws NullPointerException if the specified key, value, or unit is null
      */
-    @Nullable V putIfAbsent(K key, V value, @NonNegative long duration, TimeUnit unit);
+    @Nullable V putIfAbsent(K key, V value, long duration, TimeUnit unit);
 
     /**
      * Associates the {@code value} with the {@code key} in this cache if the specified key is not
@@ -624,7 +628,7 @@ default void setExpiresAfter(K key, Duration duration) {
      * @throws IllegalArgumentException if {@code duration} is negative
      * @throws NullPointerException if the specified key, value, or unit is null
      */
-    @Nullable V put(K key, V value, @NonNegative long duration, TimeUnit unit);
+    @Nullable V put(K key, V value, long duration, TimeUnit unit);
 
     /**
      * Associates the {@code value} with the {@code key} in this cache. If the cache previously
@@ -667,8 +671,8 @@ default void setExpiresAfter(K key, Duration duration) {
      * @throws RuntimeException or Error if the remappingFunction does so, in which case the mapping
      *         is unchanged
      */
-    default @PolyNull V compute(K key,
-        BiFunction<? super K, ? super V, ? extends @PolyNull V> remappingFunction,
+    default @Nullable V compute(K key,
+        BiFunction<? super K, ? super V, ? extends @Nullable V> remappingFunction,
         Duration duration) {
       // This method was added & implemented in version 3.0.6
       throw new UnsupportedOperationException();
@@ -687,8 +691,9 @@ default void setExpiresAfter(K key, Duration duration) {
      * @param limit the maximum size of the returned map (use {@link Integer#MAX_VALUE} to disregard
      *        the limit)
      * @return a snapshot view of the cache from the oldest entry to the youngest
+     * @throws IllegalArgumentException if the limit specified is negative
      */
-    Map<K, V> oldest(@NonNegative int limit);
+    Map<K, V> oldest(int limit);
 
     /**
      * Returns the computed result from the ordered traversal of the cache entries. The oorder of
@@ -730,8 +735,9 @@ default <T> T oldest(Function<Stream<CacheEntry<K, V>>, T> mappingFunction) {
      * @param limit the maximum size of the returned map (use {@link Integer#MAX_VALUE} to disregard
      *        the limit)
      * @return a snapshot view of the cache from the youngest entry to the oldest
+     * @throws IllegalArgumentException if the limit specified is negative
      */
-    Map<K, V> youngest(@NonNegative int limit);
+    Map<K, V> youngest(int limit);
 
     /**
      * Returns the computed result from the ordered traversal of the cache entries. The order of
@@ -813,7 +819,6 @@ default Optional<Duration> ageOf(K key) {
      * @return the length of time after which an entry is eligible to be reloaded
      * @throws NullPointerException if the unit is null
      */
-    @NonNegative
     long getRefreshesAfter(TimeUnit unit);
 
     /**
@@ -837,7 +842,7 @@ default Duration getRefreshesAfter() {
      * @throws IllegalArgumentException if {@code duration} is negative
      * @throws NullPointerException if the unit is null
      */
-    void setRefreshesAfter(@NonNegative long duration, TimeUnit unit);
+    void setRefreshesAfter(long duration, TimeUnit unit);
 
     /**
      * Specifies that each entry should be eligible for reloading once a fixed duration has elapsed.
@@ -861,6 +866,7 @@ default void setRefreshesAfter(Duration duration) {
    * @param <K> the type of keys
    * @param <V> the type of values
    */
+  @NullMarked
   interface CacheEntry<K, V> extends Map.Entry<K, V> {
 
     /**
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/References.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/References.java
index 02cb98f3b3..b9d868ed1a 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/References.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/References.java
@@ -23,7 +23,7 @@
 import java.lang.ref.WeakReference;
 import java.util.Objects;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Static utility methods and classes pertaining to weak and soft references.
@@ -83,7 +83,7 @@ default boolean referenceEquals(@Nullable Object object) {
      * @return {@code true} if this object is equivalent by {@link Object#equals} as the argument;
      *         {@code false} otherwise
      */
-    default boolean objectEquals(Object object) {
+    default boolean objectEquals(@Nullable Object object) {
       if (object == this) {
         return true;
       } else if (object instanceof InternalReference<?>) {
@@ -119,7 +119,7 @@ public Object getKeyReference() {
     }
 
     @Override
-    public boolean equals(Object object) {
+    public boolean equals(@Nullable Object object) {
       return referenceEquals(object);
     }
 
@@ -160,7 +160,7 @@ public Object getKeyReference() {
     }
 
     @Override
-    public boolean equals(Object object) {
+    public boolean equals(@Nullable Object object) {
       return objectEquals(object);
     }
 
@@ -195,7 +195,7 @@ public Object getKeyReference() {
     }
 
     @Override
-    public boolean equals(Object object) {
+    public boolean equals(@Nullable Object object) {
       return referenceEquals(object);
     }
 
@@ -231,7 +231,7 @@ public Object getKeyReference() {
     }
 
     @Override
-    public boolean equals(Object object) {
+    public boolean equals(@Nullable Object object) {
       return objectEquals(object);
     }
 
@@ -272,7 +272,7 @@ public void setKeyReference(Object keyReference) {
     }
 
     @Override
-    public boolean equals(Object object) {
+    public boolean equals(@Nullable Object object) {
       return referenceEquals(object);
     }
 
@@ -313,7 +313,7 @@ public void setKeyReference(Object keyReference) {
     }
 
     @Override
-    public boolean equals(Object object) {
+    public boolean equals(@Nullable Object object) {
       return referenceEquals(object);
     }
 
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/RemovalCause.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/RemovalCause.java
index 9cc6862fb5..92f3a9947f 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/RemovalCause.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/RemovalCause.java
@@ -15,11 +15,14 @@
  */
 package com.github.benmanes.caffeine.cache;
 
+import org.jspecify.annotations.NullMarked;
+
 /**
  * The reason why a cached entry was removed.
  *
  * @author ben.manes@gmail.com (Ben Manes)
  */
+@NullMarked
 public enum RemovalCause {
 
   /**
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/RemovalListener.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/RemovalListener.java
index 963e6b2a5e..268a6b2e57 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/RemovalListener.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/RemovalListener.java
@@ -15,7 +15,8 @@
  */
 package com.github.benmanes.caffeine.cache;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.NullMarked;
+import org.jspecify.annotations.Nullable;
 
 /**
  * An object that can receive a notification when an entry is removed from a cache. The removal
@@ -32,6 +33,7 @@
  * @param <V> the most general type of values this listener can listen for; for example
  *        {@code Object} if any value is acceptable
  */
+@NullMarked
 @FunctionalInterface
 public interface RemovalListener<K, V> {
 
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Scheduler.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Scheduler.java
index e619c9040e..85f43b0666 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Scheduler.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Scheduler.java
@@ -26,11 +26,15 @@
 import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.TimeUnit;
 
+import org.jspecify.annotations.NullMarked;
+import org.jspecify.annotations.Nullable;
+
 /**
  * A scheduler that submits a task to an executor after a given delay.
  *
  * @author ben.manes@gmail.com (Ben Manes)
  */
+@NullMarked
 @FunctionalInterface
 public interface Scheduler {
 
@@ -43,7 +47,8 @@ public interface Scheduler {
    * @param unit a {@code TimeUnit} determining how to interpret the {@code delay} parameter
    * @return a scheduled future representing the pending submission of the task
    */
-  Future<?> schedule(Executor executor, Runnable command, long delay, TimeUnit unit);
+  Future<? extends @Nullable Object> schedule(
+      Executor executor, Runnable command, long delay, TimeUnit unit);
 
   /**
    * Returns a scheduler that always returns a successfully completed future.
@@ -112,13 +117,14 @@ final class ExecutorServiceScheduler implements Scheduler, Serializable {
   }
 
   @Override
-  public Future<?> schedule(Executor executor, Runnable command, long delay, TimeUnit unit) {
+  public Future<? extends @Nullable Object> schedule(
+      Executor executor, Runnable command, long delay, TimeUnit unit) {
     requireNonNull(executor);
     requireNonNull(command);
     requireNonNull(unit);
 
     if (scheduledExecutorService.isShutdown()) {
-      return DisabledFuture.INSTANCE;
+      return DisabledFuture.instance();
     }
     return scheduledExecutorService.schedule(() -> {
       try {
@@ -143,13 +149,14 @@ final class GuardedScheduler implements Scheduler, Serializable {
   }
 
   @Override
-  public Future<?> schedule(Executor executor, Runnable command, long delay, TimeUnit unit) {
+  public Future<? extends @Nullable Object> schedule(
+      Executor executor, Runnable command, long delay, TimeUnit unit) {
     try {
-      Future<?> future = delegate.schedule(executor, command, delay, unit);
-      return (future == null) ? DisabledFuture.INSTANCE : future;
+      var future = delegate.schedule(executor, command, delay, unit);
+      return (future == null) ? DisabledFuture.instance() : future;
     } catch (Throwable t) {
       logger.log(Level.WARNING, "Exception thrown by scheduler; discarded task", t);
-      return DisabledFuture.INSTANCE;
+      return DisabledFuture.instance();
     }
   }
 }
@@ -158,18 +165,24 @@ enum DisabledScheduler implements Scheduler {
   INSTANCE;
 
   @Override
-  public Future<Void> schedule(Executor executor, Runnable command, long delay, TimeUnit unit) {
+  public Future<? extends @Nullable Object> schedule(
+      Executor executor, Runnable command, long delay, TimeUnit unit) {
     requireNonNull(executor);
     requireNonNull(command);
     requireNonNull(unit);
-    return DisabledFuture.INSTANCE;
+    return DisabledFuture.instance();
   }
 }
 
 @SuppressWarnings("CheckedExceptionNotThrown")
-enum DisabledFuture implements Future<Void> {
+enum DisabledFuture implements Future<@Nullable Void> {
   INSTANCE;
 
+  @SuppressWarnings("NullAway")
+  static Future<? extends @Nullable Object> instance() {
+    return INSTANCE;
+  }
+
   @Override public boolean isDone() {
     return true;
   }
@@ -179,11 +192,11 @@ enum DisabledFuture implements Future<Void> {
   @Override public boolean cancel(boolean mayInterruptIfRunning) {
     return false;
   }
-  @Override public Void get(long timeout, TimeUnit unit) {
+  @Override public @Nullable Void get(long timeout, TimeUnit unit) {
     requireNonNull(unit);
     return null;
   }
-  @Override public Void get() {
+  @Override public @Nullable Void get() {
     return null;
   }
 }
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/SerializationProxy.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/SerializationProxy.java
index 2b513a2b54..6ff4ba385e 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/SerializationProxy.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/SerializationProxy.java
@@ -20,7 +20,7 @@
 import java.io.Serializable;
 import java.time.Duration;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Serializes the configuration of the cache, reconstituting it as a {@link Cache},
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/SnapshotEntry.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/SnapshotEntry.java
index 4f4e7db6ba..da44b7ebda 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/SnapshotEntry.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/SnapshotEntry.java
@@ -19,6 +19,8 @@
 
 import java.util.Map;
 
+import org.jspecify.annotations.Nullable;
+
 import com.github.benmanes.caffeine.cache.Policy.CacheEntry;
 import com.google.errorprone.annotations.Immutable;
 
@@ -59,7 +61,7 @@ class SnapshotEntry<K, V> implements CacheEntry<K, V> {
   @Override public long snapshotAt() {
     return snapshot;
   }
-  @Override public boolean equals(Object o) {
+  @Override public boolean equals(@Nullable Object o) {
     if (o == this) {
       return true;
     } else if (!(o instanceof Map.Entry)) {
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/StripedBuffer.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/StripedBuffer.java
index c95ede8d87..b310b3fe10 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/StripedBuffer.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/StripedBuffer.java
@@ -27,7 +27,7 @@
 import java.util.Arrays;
 import java.util.function.Consumer;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.google.errorprone.annotations.Var;
 
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Ticker.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Ticker.java
index 4e6d687a69..0474361b4b 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Ticker.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Ticker.java
@@ -15,12 +15,15 @@
  */
 package com.github.benmanes.caffeine.cache;
 
+import org.jspecify.annotations.NullMarked;
+
 /**
  * A time source that returns a time value representing the number of nanoseconds elapsed since some
  * fixed but arbitrary point in time.
  *
  * @author ben.manes@gmail.com (Ben Manes)
  */
+@NullMarked
 @FunctionalInterface
 public interface Ticker {
 
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/TimerWheel.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/TimerWheel.java
index df9911920b..7f875682d3 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/TimerWheel.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/TimerWheel.java
@@ -23,7 +23,7 @@
 import java.util.NoSuchElementException;
 import java.util.concurrent.TimeUnit;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.google.errorprone.annotations.Var;
 
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/UnboundedLocalCache.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/UnboundedLocalCache.java
index 49a4883891..be69e5c4b7 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/UnboundedLocalCache.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/UnboundedLocalCache.java
@@ -50,7 +50,7 @@
 import java.util.function.Function;
 import java.util.function.Predicate;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.stats.StatsCounter;
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
@@ -545,7 +545,7 @@ public boolean replace(K key, V oldValue, V newValue, boolean shouldDiscardRefre
 
   @Override
   @SuppressWarnings("EqualsWhichDoesntCheckParameterClass")
-  public boolean equals(Object o) {
+  public boolean equals(@Nullable Object o) {
     return (o == this) || data.equals(o);
   }
 
@@ -1041,9 +1041,12 @@ public UnboundedLocalCache<K, V> cache() {
 
     @Override
     public Policy<K, V> policy() {
-      return (policy == null)
-          ? (policy = new UnboundedPolicy<>(cache, identity()))
-          : policy;
+      if (policy == null) {
+        @SuppressWarnings("NullAway")
+        Function<@Nullable V, @Nullable V> identity = identity();
+        policy = new UnboundedPolicy<>(cache, identity);
+      }
+      return policy;
     }
 
     private void readObject(ObjectInputStream stream) throws InvalidObjectException {
@@ -1189,8 +1192,8 @@ public Policy<K, V> policy() {
       @SuppressWarnings("unchecked")
       var castCache = (UnboundedLocalCache<K, V>) cache;
       Function<CompletableFuture<V>, @Nullable V> transformer = Async::getIfReady;
-      @SuppressWarnings("unchecked")
-      var castTransformer = (Function<V, V>) transformer;
+      @SuppressWarnings({"NullAway", "unchecked", "Varifier"})
+      Function<@Nullable V, @Nullable V> castTransformer = (Function<V, V>) transformer;
       return (policy == null)
           ? (policy = new UnboundedPolicy<>(castCache, castTransformer))
           : policy;
@@ -1242,8 +1245,8 @@ public Policy<K, V> policy() {
       @SuppressWarnings("unchecked")
       var castCache = (UnboundedLocalCache<K, V>) cache;
       Function<CompletableFuture<V>, @Nullable V> transformer = Async::getIfReady;
-      @SuppressWarnings("unchecked")
-      var castTransformer = (Function<V, V>) transformer;
+      @SuppressWarnings({"NullAway", "unchecked", "Varifier"})
+      Function<@Nullable V, @Nullable V> castTransformer = (Function<V, V>) transformer;
       return (policy == null)
           ? (policy = new UnboundedPolicy<>(castCache, castTransformer))
           : policy;
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Weigher.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Weigher.java
index 8b7cac4561..d65a87fbfb 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Weigher.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/Weigher.java
@@ -20,7 +20,7 @@
 
 import java.io.Serializable;
 
-import org.checkerframework.checker.index.qual.NonNegative;
+import org.jspecify.annotations.NullMarked;
 
 /**
  * Calculates the weights of cache entries. The total weight threshold is used to determine when an
@@ -30,6 +30,7 @@
  * @param <V> the type of values
  * @author ben.manes@gmail.com (Ben Manes)
  */
+@NullMarked
 @FunctionalInterface
 public interface Weigher<K, V> {
 
@@ -41,7 +42,6 @@ public interface Weigher<K, V> {
    * @param value the value to weigh
    * @return the weight of the entry; must be non-negative
    */
-  @NonNegative
   int weigh(K key, V value);
 
   /**
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/WriteOrderDeque.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/WriteOrderDeque.java
index ead6fe7fb5..b83c3c2a2d 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/WriteOrderDeque.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/WriteOrderDeque.java
@@ -17,7 +17,7 @@
 
 import java.util.Deque;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.WriteOrderDeque.WriteOrder;
 
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/package-info.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/package-info.java
index 0cb37b81bb..e86728caae 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/package-info.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/package-info.java
@@ -38,14 +38,10 @@
  *
  * @author ben.manes@gmail.com (Ben Manes)
  */
+@NullMarked
 @CheckReturnValue
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.FIELD)
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.PARAMETER)
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.RETURN)
 package com.github.benmanes.caffeine.cache;
 
-import org.checkerframework.checker.nullness.qual.NonNull;
-import org.checkerframework.framework.qual.DefaultQualifier;
-import org.checkerframework.framework.qual.TypeUseLocation;
+import org.jspecify.annotations.NullMarked;
 
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/stats/CacheStats.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/stats/CacheStats.java
index d22feda6d8..f75a7607d2 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/stats/CacheStats.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/stats/CacheStats.java
@@ -17,8 +17,8 @@
 
 import java.util.Objects;
 
-import org.checkerframework.checker.index.qual.NonNegative;
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.NullMarked;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.Cache;
 import com.github.benmanes.caffeine.cache.LoadingCache;
@@ -61,6 +61,7 @@
  * @author ben.manes@gmail.com (Ben Manes)
  */
 @Immutable
+@NullMarked
 public final class CacheStats {
   private static final CacheStats EMPTY_STATS = CacheStats.of(0L, 0L, 0L, 0L, 0L, 0L, 0L);
 
@@ -72,10 +73,8 @@ public final class CacheStats {
   private final long evictionCount;
   private final long evictionWeight;
 
-  private CacheStats(@NonNegative long hitCount, @NonNegative long missCount,
-      @NonNegative long loadSuccessCount, @NonNegative long loadFailureCount,
-      @NonNegative long totalLoadTime, @NonNegative long evictionCount,
-      @NonNegative long evictionWeight) {
+  private CacheStats(long hitCount, long missCount, long loadSuccessCount, long loadFailureCount,
+      long totalLoadTime, long evictionCount, long evictionWeight) {
     if ((hitCount < 0) || (missCount < 0) || (loadSuccessCount < 0) || (loadFailureCount < 0)
         || (totalLoadTime < 0) || (evictionCount < 0) || (evictionWeight < 0)) {
       throw new IllegalArgumentException();
@@ -100,11 +99,10 @@ private CacheStats(@NonNegative long hitCount, @NonNegative long missCount,
    * @param evictionCount the number of entries evicted from the cache
    * @param evictionWeight the sum of weights of entries evicted from the cache
    * @return a {@code CacheStats} representing the specified statistics
+   * @throws IllegalArgumentException if the metric is negative
    */
-  public static CacheStats of(@NonNegative long hitCount, @NonNegative long missCount,
-      @NonNegative long loadSuccessCount, @NonNegative long loadFailureCount,
-      @NonNegative long totalLoadTime, @NonNegative long evictionCount,
-      @NonNegative long evictionWeight) {
+  public static CacheStats of(long hitCount, long missCount, long loadSuccessCount,
+      long loadFailureCount, long totalLoadTime, long evictionCount, long evictionWeight) {
     // Many parameters of the same type in a row is a bad thing, but this class is not constructed
     // by end users and is too fine-grained for a builder.
     return new CacheStats(hitCount, missCount, loadSuccessCount,
@@ -130,7 +128,7 @@ public static CacheStats empty() {
    *
    * @return the {@code hitCount + missCount}
    */
-  public @NonNegative long requestCount() {
+  public long requestCount() {
     return saturatedAdd(hitCount, missCount);
   }
 
@@ -139,7 +137,7 @@ public static CacheStats empty() {
    *
    * @return the number of times {@link Cache} lookup methods have returned a cached value
    */
-  public @NonNegative long hitCount() {
+  public long hitCount() {
     return hitCount;
   }
 
@@ -150,7 +148,7 @@ public static CacheStats empty() {
    *
    * @return the ratio of cache requests which were hits
    */
-  public @NonNegative double hitRate() {
+  public double hitRate() {
     long requestCount = requestCount();
     return (requestCount == 0) ? 1.0 : (double) hitCount / requestCount;
   }
@@ -164,7 +162,7 @@ public static CacheStats empty() {
    * @return the number of times {@link Cache} lookup methods have returned an uncached (newly
    *         loaded) value, or null
    */
-  public @NonNegative long missCount() {
+  public long missCount() {
     return missCount;
   }
 
@@ -179,7 +177,7 @@ public static CacheStats empty() {
    *
    * @return the ratio of cache requests which were misses
    */
-  public @NonNegative double missRate() {
+  public double missRate() {
     long requestCount = requestCount();
     return (requestCount == 0) ? 0.0 : (double) missCount / requestCount;
   }
@@ -195,7 +193,7 @@ public static CacheStats empty() {
    *
    * @return the {@code loadSuccessCount + loadFailureCount}
    */
-  public @NonNegative long loadCount() {
+  public long loadCount() {
     return saturatedAdd(loadSuccessCount, loadFailureCount);
   }
 
@@ -208,7 +206,7 @@ public static CacheStats empty() {
    *
    * @return the number of times {@link Cache} lookup methods have successfully loaded a new value
    */
-  public @NonNegative long loadSuccessCount() {
+  public long loadSuccessCount() {
     return loadSuccessCount;
   }
 
@@ -221,7 +219,7 @@ public static CacheStats empty() {
    *
    * @return the number of times {@link Cache} lookup methods failed to load a new value
    */
-  public @NonNegative long loadFailureCount() {
+  public long loadFailureCount() {
     return loadFailureCount;
   }
 
@@ -236,7 +234,7 @@ public static CacheStats empty() {
    *
    * @return the ratio of cache loading attempts which threw exceptions
    */
-  public @NonNegative double loadFailureRate() {
+  public double loadFailureRate() {
     long totalLoadCount = saturatedAdd(loadSuccessCount, loadFailureCount);
     return (totalLoadCount == 0) ? 0.0 : (double) loadFailureCount / totalLoadCount;
   }
@@ -248,7 +246,7 @@ public static CacheStats empty() {
    *
    * @return the total number of nanoseconds the cache has spent loading new values
    */
-  public @NonNegative long totalLoadTime() {
+  public long totalLoadTime() {
     return totalLoadTime;
   }
 
@@ -262,7 +260,7 @@ public static CacheStats empty() {
    *
    * @return the average number of nanoseconds spent loading new values
    */
-  public @NonNegative double averageLoadPenalty() {
+  public double averageLoadPenalty() {
     long totalLoadCount = saturatedAdd(loadSuccessCount, loadFailureCount);
     return (totalLoadCount == 0) ? 0.0 : (double) totalLoadTime / totalLoadCount;
   }
@@ -273,7 +271,7 @@ public static CacheStats empty() {
    *
    * @return the number of times an entry has been evicted
    */
-  public @NonNegative long evictionCount() {
+  public long evictionCount() {
     return evictionCount;
   }
 
@@ -283,7 +281,7 @@ public static CacheStats empty() {
    *
    * @return the sum of weights of evicted entities
    */
-  public @NonNegative long evictionWeight() {
+  public long evictionWeight() {
     return evictionWeight;
   }
 
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/stats/ConcurrentStatsCounter.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/stats/ConcurrentStatsCounter.java
index 545610d3b8..af3063ce69 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/stats/ConcurrentStatsCounter.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/stats/ConcurrentStatsCounter.java
@@ -19,6 +19,8 @@
 
 import java.util.concurrent.atomic.LongAdder;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.github.benmanes.caffeine.cache.Cache;
 import com.github.benmanes.caffeine.cache.RemovalCause;
 
@@ -27,6 +29,7 @@
  *
  * @author ben.manes@gmail.com (Ben Manes)
  */
+@NullMarked
 public final class ConcurrentStatsCounter implements StatsCounter {
   private final LongAdder hitCount;
   private final LongAdder missCount;
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/stats/DisabledStatsCounter.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/stats/DisabledStatsCounter.java
index 905cad3782..31c927c5b0 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/stats/DisabledStatsCounter.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/stats/DisabledStatsCounter.java
@@ -17,8 +17,6 @@
 
 import static java.util.Objects.requireNonNull;
 
-import org.checkerframework.checker.index.qual.NonNegative;
-
 import com.github.benmanes.caffeine.cache.RemovalCause;
 
 /**
@@ -42,7 +40,7 @@ public void recordLoadSuccess(long loadTime) {}
   public void recordLoadFailure(long loadTime) {}
 
   @Override
-  public void recordEviction(@NonNegative int weight, RemovalCause cause) {
+  public void recordEviction(int weight, RemovalCause cause) {
     requireNonNull(cause);
   }
 
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/stats/StatsCounter.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/stats/StatsCounter.java
index d346ee7be8..5b44a38b3c 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/stats/StatsCounter.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/stats/StatsCounter.java
@@ -17,7 +17,7 @@
 
 import java.util.Map;
 
-import org.checkerframework.checker.index.qual.NonNegative;
+import org.jspecify.annotations.NullMarked;
 
 import com.github.benmanes.caffeine.cache.Cache;
 import com.github.benmanes.caffeine.cache.RemovalCause;
@@ -28,6 +28,7 @@
  *
  * @author ben.manes@gmail.com (Ben Manes)
  */
+@NullMarked
 public interface StatsCounter {
 
   /**
@@ -35,7 +36,7 @@ public interface StatsCounter {
    *
    * @param count the number of hits to record
    */
-  void recordHits(@NonNegative int count);
+  void recordHits(int count);
 
   /**
    * Records cache misses. This should be called when a cache request returns a value that was not
@@ -47,7 +48,7 @@ public interface StatsCounter {
    *
    * @param count the number of misses to record
    */
-  void recordMisses(@NonNegative int count);
+  void recordMisses(int count);
 
   /**
    * Records the successful load of a new entry. This method should be called when a cache request
@@ -57,7 +58,7 @@ public interface StatsCounter {
    *
    * @param loadTime the number of nanoseconds the cache spent computing or retrieving the new value
    */
-  void recordLoadSuccess(@NonNegative long loadTime);
+  void recordLoadSuccess(long loadTime);
 
   /**
    * Records the failed load of a new entry. This method should be called when a cache request
@@ -68,7 +69,7 @@ public interface StatsCounter {
    * @param loadTime the number of nanoseconds the cache spent computing or retrieving the new value
    *        prior to discovering the value doesn't exist or an exception being thrown
    */
-  void recordLoadFailure(@NonNegative long loadTime);
+  void recordLoadFailure(long loadTime);
 
   /**
    * Records the eviction of an entry from the cache. This should only been called when an entry is
@@ -78,7 +79,7 @@ public interface StatsCounter {
    * @param weight the weight of the evicted entry
    * @param cause the reason for which the entry was removed
    */
-  void recordEviction(@NonNegative int weight, RemovalCause cause);
+  void recordEviction(int weight, RemovalCause cause);
 
   /**
    * Returns a snapshot of this counter's values. Note that this may be an inconsistent view, as it
diff --git a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/stats/package-info.java b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/stats/package-info.java
index e3c4d5017b..4daff4f0be 100644
--- a/caffeine/src/main/java/com/github/benmanes/caffeine/cache/stats/package-info.java
+++ b/caffeine/src/main/java/com/github/benmanes/caffeine/cache/stats/package-info.java
@@ -19,14 +19,10 @@
  *
  * @author ben.manes@gmail.com (Ben Manes)
  */
+@NullMarked
 @CheckReturnValue
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.FIELD)
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.PARAMETER)
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.RETURN)
 package com.github.benmanes.caffeine.cache.stats;
 
-import org.checkerframework.checker.nullness.qual.NonNull;
-import org.checkerframework.framework.qual.DefaultQualifier;
-import org.checkerframework.framework.qual.TypeUseLocation;
+import org.jspecify.annotations.NullMarked;
 
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/caffeine/src/main/java/module-info.java b/caffeine/src/main/java/module-info.java
index 28fbf809f8..b9ba210c0a 100644
--- a/caffeine/src/main/java/module-info.java
+++ b/caffeine/src/main/java/module-info.java
@@ -4,5 +4,5 @@
   exports com.github.benmanes.caffeine.cache.stats;
 
   requires static com.google.errorprone.annotations;
-  requires static org.checkerframework.checker.qual;
+  requires static org.jspecify;
 }
diff --git a/caffeine/src/test/java/com/github/benmanes/caffeine/apache/package-info.java b/caffeine/src/test/java/com/github/benmanes/caffeine/apache/package-info.java
index 9270e849a5..b4224b36a3 100644
--- a/caffeine/src/test/java/com/github/benmanes/caffeine/apache/package-info.java
+++ b/caffeine/src/test/java/com/github/benmanes/caffeine/apache/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.apache;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/caffeine/src/test/java/com/github/benmanes/caffeine/cache/CacheTest.java b/caffeine/src/test/java/com/github/benmanes/caffeine/cache/CacheTest.java
index 9483f5a9ac..feb55527b9 100644
--- a/caffeine/src/test/java/com/github/benmanes/caffeine/cache/CacheTest.java
+++ b/caffeine/src/test/java/com/github/benmanes/caffeine/cache/CacheTest.java
@@ -55,7 +55,7 @@
 import java.util.stream.IntStream;
 
 import org.apache.commons.lang3.tuple.Triple;
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 import org.mockito.Mockito;
 import org.mockito.stubbing.Answer;
 import org.testng.annotations.Listeners;
diff --git a/caffeine/src/test/java/com/github/benmanes/caffeine/cache/LinkedDequeTests.java b/caffeine/src/test/java/com/github/benmanes/caffeine/cache/LinkedDequeTests.java
index 758696c627..38c579cf53 100644
--- a/caffeine/src/test/java/com/github/benmanes/caffeine/cache/LinkedDequeTests.java
+++ b/caffeine/src/test/java/com/github/benmanes/caffeine/cache/LinkedDequeTests.java
@@ -20,7 +20,7 @@
 import java.util.Queue;
 import java.util.function.Supplier;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.AccessOrderDeque.AccessOrder;
 import com.github.benmanes.caffeine.cache.WriteOrderDeque.WriteOrder;
diff --git a/caffeine/src/test/java/com/github/benmanes/caffeine/cache/TimerWheelTest.java b/caffeine/src/test/java/com/github/benmanes/caffeine/cache/TimerWheelTest.java
index e89d4ab76d..4141be2b87 100644
--- a/caffeine/src/test/java/com/github/benmanes/caffeine/cache/TimerWheelTest.java
+++ b/caffeine/src/test/java/com/github/benmanes/caffeine/cache/TimerWheelTest.java
@@ -44,7 +44,7 @@
 import java.util.stream.IntStream;
 import java.util.stream.LongStream;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 import org.mockito.ArgumentCaptor;
 import org.mockito.Captor;
 import org.mockito.Mock;
diff --git a/caffeine/src/test/java/com/github/benmanes/caffeine/cache/buffer/package-info.java b/caffeine/src/test/java/com/github/benmanes/caffeine/cache/buffer/package-info.java
index 1974f97a7b..9171e2bf78 100644
--- a/caffeine/src/test/java/com/github/benmanes/caffeine/cache/buffer/package-info.java
+++ b/caffeine/src/test/java/com/github/benmanes/caffeine/cache/buffer/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.buffer;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/caffeine/src/test/java/com/github/benmanes/caffeine/cache/issues/package-info.java b/caffeine/src/test/java/com/github/benmanes/caffeine/cache/issues/package-info.java
index 05d7842b0d..52502dad6a 100644
--- a/caffeine/src/test/java/com/github/benmanes/caffeine/cache/issues/package-info.java
+++ b/caffeine/src/test/java/com/github/benmanes/caffeine/cache/issues/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.issues;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/caffeine/src/test/java/com/github/benmanes/caffeine/cache/package-info.java b/caffeine/src/test/java/com/github/benmanes/caffeine/cache/package-info.java
index 6a536374b0..a00ec4f1f7 100644
--- a/caffeine/src/test/java/com/github/benmanes/caffeine/cache/package-info.java
+++ b/caffeine/src/test/java/com/github/benmanes/caffeine/cache/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/caffeine/src/test/java/com/github/benmanes/caffeine/cache/stats/package-info.java b/caffeine/src/test/java/com/github/benmanes/caffeine/cache/stats/package-info.java
index c5d91d8e79..d552762417 100644
--- a/caffeine/src/test/java/com/github/benmanes/caffeine/cache/stats/package-info.java
+++ b/caffeine/src/test/java/com/github/benmanes/caffeine/cache/stats/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.stats;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/caffeine/src/test/java/com/github/benmanes/caffeine/cache/testing/CacheContext.java b/caffeine/src/test/java/com/github/benmanes/caffeine/cache/testing/CacheContext.java
index faf0e0543b..016c317c0b 100644
--- a/caffeine/src/test/java/com/github/benmanes/caffeine/cache/testing/CacheContext.java
+++ b/caffeine/src/test/java/com/github/benmanes/caffeine/cache/testing/CacheContext.java
@@ -30,7 +30,7 @@
 import java.util.concurrent.ThreadLocalRandom;
 import java.util.function.Function;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.AsyncCache;
 import com.github.benmanes.caffeine.cache.AsyncCacheLoader;
diff --git a/caffeine/src/test/java/com/github/benmanes/caffeine/cache/testing/RemovalNotification.java b/caffeine/src/test/java/com/github/benmanes/caffeine/cache/testing/RemovalNotification.java
index f8e6709853..85df025a19 100644
--- a/caffeine/src/test/java/com/github/benmanes/caffeine/cache/testing/RemovalNotification.java
+++ b/caffeine/src/test/java/com/github/benmanes/caffeine/cache/testing/RemovalNotification.java
@@ -19,7 +19,7 @@
 
 import java.util.AbstractMap.SimpleImmutableEntry;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.RemovalCause;
 import com.google.errorprone.annotations.Immutable;
diff --git a/caffeine/src/test/java/com/github/benmanes/caffeine/cache/testing/package-info.java b/caffeine/src/test/java/com/github/benmanes/caffeine/cache/testing/package-info.java
index a63f5a0e1c..a0b3db4fd2 100644
--- a/caffeine/src/test/java/com/github/benmanes/caffeine/cache/testing/package-info.java
+++ b/caffeine/src/test/java/com/github/benmanes/caffeine/cache/testing/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.testing;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/caffeine/src/test/java/com/github/benmanes/caffeine/eclipse/acceptance/package-info.java b/caffeine/src/test/java/com/github/benmanes/caffeine/eclipse/acceptance/package-info.java
index 4462c3fc04..d60faccb8e 100644
--- a/caffeine/src/test/java/com/github/benmanes/caffeine/eclipse/acceptance/package-info.java
+++ b/caffeine/src/test/java/com/github/benmanes/caffeine/eclipse/acceptance/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.eclipse.acceptance;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/caffeine/src/test/java/com/github/benmanes/caffeine/eclipse/mutable/package-info.java b/caffeine/src/test/java/com/github/benmanes/caffeine/eclipse/mutable/package-info.java
index 185eb6960e..7e35d237c6 100644
--- a/caffeine/src/test/java/com/github/benmanes/caffeine/eclipse/mutable/package-info.java
+++ b/caffeine/src/test/java/com/github/benmanes/caffeine/eclipse/mutable/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.eclipse.mutable;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/caffeine/src/test/java/com/github/benmanes/caffeine/eclipse/package-info.java b/caffeine/src/test/java/com/github/benmanes/caffeine/eclipse/package-info.java
index 3dff8e7ad7..5147944a3f 100644
--- a/caffeine/src/test/java/com/github/benmanes/caffeine/eclipse/package-info.java
+++ b/caffeine/src/test/java/com/github/benmanes/caffeine/eclipse/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.eclipse;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/caffeine/src/test/java/com/github/benmanes/caffeine/fuzz/package-info.java b/caffeine/src/test/java/com/github/benmanes/caffeine/fuzz/package-info.java
new file mode 100644
index 0000000000..99f4496c8a
--- /dev/null
+++ b/caffeine/src/test/java/com/github/benmanes/caffeine/fuzz/package-info.java
@@ -0,0 +1,7 @@
+@NullMarked
+@CheckReturnValue
+package com.github.benmanes.caffeine.fuzz;
+
+import org.jspecify.annotations.NullMarked;
+
+import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/caffeine/src/test/java/com/github/benmanes/caffeine/google/package-info.java b/caffeine/src/test/java/com/github/benmanes/caffeine/google/package-info.java
index 3fac419333..b20cadb6ad 100644
--- a/caffeine/src/test/java/com/github/benmanes/caffeine/google/package-info.java
+++ b/caffeine/src/test/java/com/github/benmanes/caffeine/google/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.google;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/caffeine/src/test/java/com/github/benmanes/caffeine/jsr166/JSR166TestCase.java b/caffeine/src/test/java/com/github/benmanes/caffeine/jsr166/JSR166TestCase.java
index 9a255cff09..905872dfaa 100644
--- a/caffeine/src/test/java/com/github/benmanes/caffeine/jsr166/JSR166TestCase.java
+++ b/caffeine/src/test/java/com/github/benmanes/caffeine/jsr166/JSR166TestCase.java
@@ -99,7 +99,7 @@
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.regex.Pattern;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import junit.framework.Test;
 import junit.framework.TestCase;
diff --git a/caffeine/src/test/java/com/github/benmanes/caffeine/jsr166/package-info.java b/caffeine/src/test/java/com/github/benmanes/caffeine/jsr166/package-info.java
index 21a610d0af..2bdc3c41d3 100644
--- a/caffeine/src/test/java/com/github/benmanes/caffeine/jsr166/package-info.java
+++ b/caffeine/src/test/java/com/github/benmanes/caffeine/jsr166/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.jsr166;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/caffeine/src/test/java/com/github/benmanes/caffeine/lincheck/package-info.java b/caffeine/src/test/java/com/github/benmanes/caffeine/lincheck/package-info.java
index 7b4d6d1976..352232d65d 100644
--- a/caffeine/src/test/java/com/github/benmanes/caffeine/lincheck/package-info.java
+++ b/caffeine/src/test/java/com/github/benmanes/caffeine/lincheck/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.lincheck;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/caffeine/src/test/java/com/github/benmanes/caffeine/package-info.java b/caffeine/src/test/java/com/github/benmanes/caffeine/package-info.java
index 7e490e3225..3339cf3563 100644
--- a/caffeine/src/test/java/com/github/benmanes/caffeine/package-info.java
+++ b/caffeine/src/test/java/com/github/benmanes/caffeine/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/caffeine/src/test/java/com/github/benmanes/caffeine/testing/package-info.java b/caffeine/src/test/java/com/github/benmanes/caffeine/testing/package-info.java
index 93eeda5244..3e1740f3b6 100644
--- a/caffeine/src/test/java/com/github/benmanes/caffeine/testing/package-info.java
+++ b/caffeine/src/test/java/com/github/benmanes/caffeine/testing/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.testing;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/gradle/libs.versions.toml b/gradle/libs.versions.toml
index b1180b843c..a8754db053 100644
--- a/gradle/libs.versions.toml
+++ b/gradle/libs.versions.toml
@@ -7,7 +7,6 @@ bnd = "7.0.0"
 bouncycastle-jdk18on = "1.79"
 cache2k = "2.6.1.Final"
 caffeine = "3.1.8"
-checker-framework = "3.48.2"
 checkstyle = "10.20.1"
 coherence = "24.09"
 commons-collections4 = "4.4"
@@ -58,6 +57,7 @@ jmh = "1.37"
 jmh-plugin = "0.7.2"
 jmh-report = "0.9.6"
 joor = "0.9.15"
+jspecify = "1.0.0"
 json-bind = "1.0"
 jsoup = "1.18.1"
 junit-testng = "1.0.5"
@@ -96,7 +96,7 @@ versions = "0.51.0"
 xz = "1.10"
 ycsb = "0.17.0"
 zero-allocation-hashing = "0.27ea0"
-zstd = "1.5.6-7"
+zstd = "1.5.6-8"
 
 [libraries]
 asm-bom = { module = "org.ow2.asm:asm-bom", version.ref = "asm" }
@@ -107,7 +107,6 @@ bcel = { module = "org.apache.bcel:bcel", version.ref = "bcel" }
 bouncycastle-jdk18on = { module = "org.bouncycastle:bcprov-jdk18on", version.ref = "bouncycastle-jdk18on" }
 cache2k = { module = "org.cache2k:cache2k-core", version.ref = "cache2k" }
 caffeine = { module = "com.github.ben-manes.caffeine:caffeine", version.ref = "caffeine" }
-checker-annotations = { module = "org.checkerframework:checker-qual", version.ref = "checker-framework" }
 checkstyle = { module = "com.puppycrawl.tools:checkstyle", version.ref = "checkstyle" }
 coherence = { module = "com.oracle.coherence.ce:coherence", version.ref = "coherence" }
 commons-collections4 = { module = "org.apache.commons:commons-collections4", version.ref = "commons-collections4" }
@@ -160,6 +159,7 @@ jfreechart = { module = "org.jfree:jfreechart", version.ref = "jfreechart" }
 jgit = { module = "org.eclipse.jgit:org.eclipse.jgit", version.ref = "jgit" }
 jmh = { module = "org.openjdk.jmh:jmh-core", version.ref = "jmh" }
 joor = { module = "org.jooq:joor", version.ref = "joor" }
+jspecify = { module = "org.jspecify:jspecify", version.ref = "jspecify" }
 json-bind = { module = "javax.json.bind:javax.json.bind-api", version.ref = "json-bind" }
 jsoup = { module = "org.jsoup:jsoup", version.ref = "jsoup" }
 junit4 = { module = "junit:junit", version.ref = "junit4" }
diff --git a/gradle/plugins/src/main/kotlin/lifecycle/java-library.caffeine.gradle.kts b/gradle/plugins/src/main/kotlin/lifecycle/java-library.caffeine.gradle.kts
index f4279bcecd..5729dd717b 100644
--- a/gradle/plugins/src/main/kotlin/lifecycle/java-library.caffeine.gradle.kts
+++ b/gradle/plugins/src/main/kotlin/lifecycle/java-library.caffeine.gradle.kts
@@ -97,7 +97,7 @@ tasks.withType<Javadoc>().configureEach {
     addStringOption("-release", javaVersion.toString())
     addStringOption("-link-modularity-mismatch", "info")
     links(
-      "https://checkerframework.org/api/",
+      "https://jspecify.dev/docs/api/",
       "https://errorprone.info/api/latest/",
       "https://lightbend.github.io/config/latest/api/",
       "https://docs.oracle.com/en/java/javase/$javaVersion/docs/api/",
diff --git a/guava/src/main/java/com/github/benmanes/caffeine/guava/CaffeinatedGuava.java b/guava/src/main/java/com/github/benmanes/caffeine/guava/CaffeinatedGuava.java
index ae9d59c206..9f8b1c4285 100644
--- a/guava/src/main/java/com/github/benmanes/caffeine/guava/CaffeinatedGuava.java
+++ b/guava/src/main/java/com/github/benmanes/caffeine/guava/CaffeinatedGuava.java
@@ -17,6 +17,8 @@
 
 import java.lang.reflect.Method;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.github.benmanes.caffeine.cache.Caffeine;
 import com.github.benmanes.caffeine.guava.CaffeinatedGuavaLoadingCache.ExternalBulkLoader;
 import com.github.benmanes.caffeine.guava.CaffeinatedGuavaLoadingCache.ExternalSingleLoader;
@@ -31,6 +33,7 @@
  *
  * @author ben.manes@gmail.com (Ben Manes)
  */
+@NullMarked
 public final class CaffeinatedGuava {
 
   private CaffeinatedGuava() {}
diff --git a/guava/src/main/java/com/github/benmanes/caffeine/guava/CaffeinatedGuavaCache.java b/guava/src/main/java/com/github/benmanes/caffeine/guava/CaffeinatedGuavaCache.java
index 13efae59ed..833171da5a 100644
--- a/guava/src/main/java/com/github/benmanes/caffeine/guava/CaffeinatedGuavaCache.java
+++ b/guava/src/main/java/com/github/benmanes/caffeine/guava/CaffeinatedGuavaCache.java
@@ -29,7 +29,7 @@
 import java.util.function.Function;
 import java.util.function.Predicate;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.google.common.cache.Cache;
 import com.google.common.cache.CacheLoader.InvalidCacheLoadException;
diff --git a/guava/src/main/java/com/github/benmanes/caffeine/guava/CaffeinatedGuavaLoadingCache.java b/guava/src/main/java/com/github/benmanes/caffeine/guava/CaffeinatedGuavaLoadingCache.java
index c428c3d804..5be56d477f 100644
--- a/guava/src/main/java/com/github/benmanes/caffeine/guava/CaffeinatedGuavaLoadingCache.java
+++ b/guava/src/main/java/com/github/benmanes/caffeine/guava/CaffeinatedGuavaLoadingCache.java
@@ -25,7 +25,7 @@
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.Executor;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.CacheLoader;
 import com.google.common.cache.CacheLoader.InvalidCacheLoadException;
diff --git a/guava/src/main/java/com/github/benmanes/caffeine/guava/package-info.java b/guava/src/main/java/com/github/benmanes/caffeine/guava/package-info.java
index ca4d364dd3..4a851c30e1 100644
--- a/guava/src/main/java/com/github/benmanes/caffeine/guava/package-info.java
+++ b/guava/src/main/java/com/github/benmanes/caffeine/guava/package-info.java
@@ -19,14 +19,10 @@
  *
  * @author ben.manes@gmail.com (Ben Manes)
  */
+@NullMarked
 @CheckReturnValue
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.FIELD)
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.PARAMETER)
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.RETURN)
 package com.github.benmanes.caffeine.guava;
 
-import org.checkerframework.checker.nullness.qual.NonNull;
-import org.checkerframework.framework.qual.DefaultQualifier;
-import org.checkerframework.framework.qual.TypeUseLocation;
+import org.jspecify.annotations.NullMarked;
 
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/guava/src/main/java/module-info.java b/guava/src/main/java/module-info.java
index 9558b39cc6..356cebcd0c 100644
--- a/guava/src/main/java/module-info.java
+++ b/guava/src/main/java/module-info.java
@@ -5,5 +5,5 @@
   requires transitive com.google.common;
 
   requires static com.google.errorprone.annotations;
-  requires static org.checkerframework.checker.qual;
+  requires static org.jspecify;
 }
diff --git a/guava/src/test/java/com/github/benmanes/caffeine/guava/compatibility/TestingCacheLoaders.java b/guava/src/test/java/com/github/benmanes/caffeine/guava/compatibility/TestingCacheLoaders.java
index 844fdd3bec..a68bb3307d 100644
--- a/guava/src/test/java/com/github/benmanes/caffeine/guava/compatibility/TestingCacheLoaders.java
+++ b/guava/src/test/java/com/github/benmanes/caffeine/guava/compatibility/TestingCacheLoaders.java
@@ -20,7 +20,7 @@
 import java.util.Map;
 import java.util.concurrent.atomic.AtomicInteger;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.google.common.annotations.GwtCompatible;
 import com.google.common.annotations.GwtIncompatible;
diff --git a/guava/src/test/java/com/github/benmanes/caffeine/guava/compatibility/package-info.java b/guava/src/test/java/com/github/benmanes/caffeine/guava/compatibility/package-info.java
index ef87390580..8676507608 100644
--- a/guava/src/test/java/com/github/benmanes/caffeine/guava/compatibility/package-info.java
+++ b/guava/src/test/java/com/github/benmanes/caffeine/guava/compatibility/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.guava.compatibility;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/guava/src/test/java/com/github/benmanes/caffeine/guava/package-info.java b/guava/src/test/java/com/github/benmanes/caffeine/guava/package-info.java
index 5e7a01be5d..b3c9612491 100644
--- a/guava/src/test/java/com/github/benmanes/caffeine/guava/package-info.java
+++ b/guava/src/test/java/com/github/benmanes/caffeine/guava/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.guava;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/jcache/build.gradle.kts b/jcache/build.gradle.kts
index fd9433019d..5b5250d356 100644
--- a/jcache/build.gradle.kts
+++ b/jcache/build.gradle.kts
@@ -79,7 +79,7 @@ tasks.jar {
     "Automatic-Module-Name" to "com.github.benmanes.caffeine.jcache",
     "Bundle-SymbolicName" to "com.github.ben-manes.caffeine.jcache",
     "Import-Package" to listOf(
-      "!org.checkerframework.*",
+      "!org.jspecify.annotation.*",
       "!com.google.errorprone.annotations.*",
       "jakarta.inject.*;resolution:=\"optional\"",
       "*").joinToString(","),
diff --git a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/CacheFactory.java b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/CacheFactory.java
index 63c5d27860..6d6113a312 100644
--- a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/CacheFactory.java
+++ b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/CacheFactory.java
@@ -30,7 +30,7 @@
 import javax.cache.expiry.ExpiryPolicy;
 import javax.cache.integration.CacheLoader;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.Caffeine;
 import com.github.benmanes.caffeine.cache.Expiry;
diff --git a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/CacheManagerImpl.java b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/CacheManagerImpl.java
index 828540ba4e..32238fb5ca 100644
--- a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/CacheManagerImpl.java
+++ b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/CacheManagerImpl.java
@@ -33,7 +33,7 @@
 import javax.cache.configuration.Configuration;
 import javax.cache.spi.CachingProvider;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 /**
  * An implementation of JSR-107 {@link CacheManager} that manages Caffeine-based caches.
diff --git a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/CacheProxy.java b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/CacheProxy.java
index a73f918fc0..33d5f18355 100644
--- a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/CacheProxy.java
+++ b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/CacheProxy.java
@@ -59,8 +59,7 @@
 import javax.cache.processor.EntryProcessorException;
 import javax.cache.processor.EntryProcessorResult;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
-import org.checkerframework.checker.nullness.qual.PolyNull;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.Ticker;
 import com.github.benmanes.caffeine.jcache.configuration.CaffeineConfiguration;
@@ -1110,7 +1109,7 @@ protected final void requireNotClosed() {
    * @return a copy of the object if storing by value or the same instance if by reference
    */
   @SuppressWarnings("NullAway")
-  protected final <T> @PolyNull T copyOf(@PolyNull @Nullable T object) {
+  protected final <T> T copyOf(@Nullable T object) {
     if (object == null) {
       return null;
     }
@@ -1125,7 +1124,7 @@ protected final void requireNotClosed() {
    * @return a copy of the value if storing by value or the same instance if by reference
    */
   @SuppressWarnings("NullAway")
-  protected final @PolyNull V copyValue(@PolyNull Expirable<V> expirable) {
+  protected final V copyValue(@Nullable Expirable<V> expirable) {
     if (expirable == null) {
       return null;
     }
diff --git a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/LoadingCacheProxy.java b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/LoadingCacheProxy.java
index 9c3efe979f..ce827306e9 100644
--- a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/LoadingCacheProxy.java
+++ b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/LoadingCacheProxy.java
@@ -32,7 +32,7 @@
 import javax.cache.integration.CacheLoader;
 import javax.cache.integration.CompletionListener;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.LoadingCache;
 import com.github.benmanes.caffeine.cache.Ticker;
diff --git a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/configuration/CaffeineConfiguration.java b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/configuration/CaffeineConfiguration.java
index 17faecc1bd..39aee128ee 100644
--- a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/configuration/CaffeineConfiguration.java
+++ b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/configuration/CaffeineConfiguration.java
@@ -33,7 +33,8 @@
 import javax.cache.integration.CacheLoader;
 import javax.cache.integration.CacheWriter;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.NullMarked;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.Expiry;
 import com.github.benmanes.caffeine.cache.Scheduler;
@@ -53,6 +54,7 @@
  *
  * @author ben.manes@gmail.com (Ben Manes)
  */
+@NullMarked
 public final class CaffeineConfiguration<K, V> implements CompleteConfiguration<K, V> {
   private static final Factory<Scheduler> DISABLED_SCHEDULER = Scheduler::disabledScheduler;
   private static final Factory<Copier> JAVA_COPIER = JavaSerializationCopier::new;
@@ -606,7 +608,7 @@ public CaffeineConfiguration<K, V> setWeigherFactory(
   }
 
   @Override
-  public boolean equals(Object o) {
+  public boolean equals(@Nullable Object o) {
     if (o == this) {
       return true;
     } else if (!(o instanceof CaffeineConfiguration<?, ?>)) {
diff --git a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/configuration/ConfigSource.java b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/configuration/ConfigSource.java
index 8d71f4822b..4c5d291302 100644
--- a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/configuration/ConfigSource.java
+++ b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/configuration/ConfigSource.java
@@ -17,6 +17,8 @@
 
 import java.net.URI;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.typesafe.config.Config;
 
 /**
@@ -24,6 +26,7 @@
  *
  * @author ben.manes@gmail.com (Ben Manes)
  */
+@NullMarked
 @FunctionalInterface
 public interface ConfigSource {
 
diff --git a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/configuration/FactoryCreator.java b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/configuration/FactoryCreator.java
index bab337d86c..afb1abccfe 100644
--- a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/configuration/FactoryCreator.java
+++ b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/configuration/FactoryCreator.java
@@ -17,11 +17,14 @@
 
 import javax.cache.configuration.Factory;
 
+import org.jspecify.annotations.NullMarked;
+
 /**
  * An object capable of providing factories that produce an instance for a given class name.
  *
  * @author ben.manes@gmail.com (Ben Manes)
  */
+@NullMarked
 @FunctionalInterface
 public interface FactoryCreator {
 
diff --git a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/configuration/TypesafeConfigurator.java b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/configuration/TypesafeConfigurator.java
index a8e9963cb9..5f8b3871c8 100644
--- a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/configuration/TypesafeConfigurator.java
+++ b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/configuration/TypesafeConfigurator.java
@@ -41,7 +41,8 @@
 import javax.cache.expiry.EternalExpiryPolicy;
 import javax.cache.expiry.ExpiryPolicy;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.NullMarked;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.jcache.expiry.JCacheExpiryPolicy;
 import com.google.errorprone.annotations.Var;
@@ -59,6 +60,7 @@
  *
  * @author ben.manes@gmail.com (Ben Manes)
  */
+@NullMarked
 @SuppressWarnings({"PMD.AvoidDuplicateLiterals", "PMD.MutableStaticState"})
 public final class TypesafeConfigurator {
   static final Logger logger = System.getLogger(TypesafeConfigurator.class.getName());
diff --git a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/configuration/package-info.java b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/configuration/package-info.java
index 8326354ad1..d45ee11a63 100644
--- a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/configuration/package-info.java
+++ b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/configuration/package-info.java
@@ -1,11 +1,7 @@
+@NullMarked
 @CheckReturnValue
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.FIELD)
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.PARAMETER)
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.RETURN)
 package com.github.benmanes.caffeine.jcache.configuration;
 
-import org.checkerframework.checker.nullness.qual.NonNull;
-import org.checkerframework.framework.qual.DefaultQualifier;
-import org.checkerframework.framework.qual.TypeUseLocation;
+import org.jspecify.annotations.NullMarked;
 
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/copy/AbstractCopier.java b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/copy/AbstractCopier.java
index 2216c9fff0..c3bad515e4 100644
--- a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/copy/AbstractCopier.java
+++ b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/copy/AbstractCopier.java
@@ -38,6 +38,8 @@
 import java.util.function.Function;
 import java.util.regex.Pattern;
 
+import org.jspecify.annotations.NullMarked;
+
 /**
  * A skeleton implementation where subclasses provide the serialization strategy. Serialization is
  * not performed if the type is a known immutable, an array of known immutable types, or specially
@@ -45,6 +47,7 @@
  *
  * @author ben.manes@gmail.com (Ben Manes)
  */
+@NullMarked
 @SuppressWarnings({"ImmutableMemberCollection", "JavaUtilDate", "JdkObsolete"})
 public abstract class AbstractCopier<A> implements Copier {
   private static final Map<Class<?>, Function<Object, Object>> JAVA_DEEP_COPY = Map.of(Date.class,
diff --git a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/copy/Copier.java b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/copy/Copier.java
index 31a9e154ac..c0706ded29 100644
--- a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/copy/Copier.java
+++ b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/copy/Copier.java
@@ -15,12 +15,15 @@
  */
 package com.github.benmanes.caffeine.jcache.copy;
 
+import org.jspecify.annotations.NullMarked;
+
 /**
  * An object is copied when the cache is configured with <code>storeByValue</code> to guard against
  * mutations of the key or value.
  *
  * @author ben.manes@gmail.com (Ben Manes)
  */
+@NullMarked
 @FunctionalInterface
 public interface Copier {
 
diff --git a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/copy/JavaSerializationCopier.java b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/copy/JavaSerializationCopier.java
index 0bee8a1f13..f9e1ae0bcb 100644
--- a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/copy/JavaSerializationCopier.java
+++ b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/copy/JavaSerializationCopier.java
@@ -31,6 +31,8 @@
 
 import javax.cache.CacheException;
 
+import org.jspecify.annotations.NullMarked;
+
 /**
  * A strategy that uses Java serialization if a fast path approach is not applicable.
  * <p>
@@ -40,6 +42,7 @@
  *
  * @author ben.manes@gmail.com (Ben Manes)
  */
+@NullMarked
 public class JavaSerializationCopier extends AbstractCopier<byte[]> {
 
   public JavaSerializationCopier() {
diff --git a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/copy/package-info.java b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/copy/package-info.java
index 590a2760af..5aa6b49a90 100644
--- a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/copy/package-info.java
+++ b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/copy/package-info.java
@@ -1,11 +1,7 @@
+@NullMarked
 @CheckReturnValue
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.FIELD)
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.PARAMETER)
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.RETURN)
 package com.github.benmanes.caffeine.jcache.copy;
 
-import org.checkerframework.checker.nullness.qual.NonNull;
-import org.checkerframework.framework.qual.DefaultQualifier;
-import org.checkerframework.framework.qual.TypeUseLocation;
+import org.jspecify.annotations.NullMarked;
 
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/event/EventDispatcher.java b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/event/EventDispatcher.java
index eefc170686..cdd9d839bd 100644
--- a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/event/EventDispatcher.java
+++ b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/event/EventDispatcher.java
@@ -35,7 +35,7 @@
 import javax.cache.event.CacheEntryListener;
 import javax.cache.event.EventType;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.google.errorprone.annotations.Var;
 
@@ -67,8 +67,8 @@
 public final class EventDispatcher<K, V> {
   static final Logger logger = System.getLogger(EventDispatcher.class.getName());
 
-  final ConcurrentMap<Registration<K, V>, ConcurrentMap<K, CompletableFuture<Void>>> dispatchQueues;
-  final ThreadLocal<List<CompletableFuture<Void>>> pending;
+  final ConcurrentMap<Registration<K, V>, ConcurrentMap<K, CompletableFuture<@Nullable Void>>> dispatchQueues;
+  final ThreadLocal<List<CompletableFuture<@Nullable Void>>> pending;
   final Executor executor;
 
   public EventDispatcher(Executor executor) {
@@ -195,7 +195,7 @@ public void publishExpiredQuietly(Cache<K, V> cache, K key, V value) {
    * published.
    */
   public void awaitSynchronous() {
-    List<CompletableFuture<Void>> futures = pending.get();
+    var futures = pending.get();
     if (futures.isEmpty()) {
       return;
     }
diff --git a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/event/EventTypeFilter.java b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/event/EventTypeFilter.java
index 915e4910fc..6587736e0a 100644
--- a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/event/EventTypeFilter.java
+++ b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/event/EventTypeFilter.java
@@ -28,6 +28,8 @@
 import javax.cache.event.CacheEntryRemovedListener;
 import javax.cache.event.CacheEntryUpdatedListener;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * A filter that determines if the listener can process the event type before delegating to the
  * decorated filter.
@@ -64,7 +66,7 @@ private boolean isCompatible(CacheEntryEvent<? extends K, ? extends V> event) {
   }
 
   @Override
-  public boolean equals(Object o) {
+  public boolean equals(@Nullable Object o) {
     if (o == this) {
       return true;
     } else if (!(o instanceof EventTypeFilter<?, ?>)) {
diff --git a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/event/JCacheEntryEvent.java b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/event/JCacheEntryEvent.java
index 0e62b8d977..e641296868 100644
--- a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/event/JCacheEntryEvent.java
+++ b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/event/JCacheEntryEvent.java
@@ -24,7 +24,7 @@
 import javax.cache.event.CacheEntryEvent;
 import javax.cache.event.EventType;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 /**
  * A cache event dispatched to a listener.
diff --git a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/event/JCacheEvictionListener.java b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/event/JCacheEvictionListener.java
index 856852c0e9..fadad57570 100644
--- a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/event/JCacheEvictionListener.java
+++ b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/event/JCacheEvictionListener.java
@@ -19,7 +19,7 @@
 
 import javax.cache.Cache;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.RemovalCause;
 import com.github.benmanes.caffeine.cache.RemovalListener;
diff --git a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/event/Registration.java b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/event/Registration.java
index c55ec09bb5..f00766ecf8 100644
--- a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/event/Registration.java
+++ b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/event/Registration.java
@@ -22,6 +22,8 @@
 import javax.cache.event.CacheEntryEventFilter;
 import javax.cache.event.CacheEntryListener;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * The registration of a {@link CacheEntryListener} for event dispatching.
  *
@@ -61,7 +63,7 @@ public boolean isSynchronous() {
   }
 
   @Override
-  public boolean equals(Object o) {
+  public boolean equals(@Nullable Object o) {
     if (o == this) {
       return true;
     } else if (!(o instanceof Registration)) {
diff --git a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/event/package-info.java b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/event/package-info.java
index 99258f334a..cd52195a6f 100644
--- a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/event/package-info.java
+++ b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/event/package-info.java
@@ -1,11 +1,7 @@
+@NullMarked
 @CheckReturnValue
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.FIELD)
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.PARAMETER)
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.RETURN)
 package com.github.benmanes.caffeine.jcache.event;
 
-import org.checkerframework.checker.nullness.qual.NonNull;
-import org.checkerframework.framework.qual.DefaultQualifier;
-import org.checkerframework.framework.qual.TypeUseLocation;
+import org.jspecify.annotations.NullMarked;
 
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/expiry/JCacheExpiryPolicy.java b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/expiry/JCacheExpiryPolicy.java
index f1486970d4..9b70b55b39 100644
--- a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/expiry/JCacheExpiryPolicy.java
+++ b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/expiry/JCacheExpiryPolicy.java
@@ -23,7 +23,7 @@
 import javax.cache.expiry.Duration;
 import javax.cache.expiry.ExpiryPolicy;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 /**
  * A customized expiration policy.
@@ -60,7 +60,7 @@ public Duration getExpiryForCreation() {
   }
 
   @Override
-  public boolean equals(Object o) {
+  public boolean equals(@Nullable Object o) {
     if (o == this) {
       return true;
     } else if (!(o instanceof ExpiryPolicy)) {
diff --git a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/expiry/package-info.java b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/expiry/package-info.java
index 287621f24f..9370bdeb3a 100644
--- a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/expiry/package-info.java
+++ b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/expiry/package-info.java
@@ -1,11 +1,7 @@
+@NullMarked
 @CheckReturnValue
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.FIELD)
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.PARAMETER)
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.RETURN)
 package com.github.benmanes.caffeine.jcache.expiry;
 
-import org.checkerframework.checker.nullness.qual.NonNull;
-import org.checkerframework.framework.qual.DefaultQualifier;
-import org.checkerframework.framework.qual.TypeUseLocation;
+import org.jspecify.annotations.NullMarked;
 
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/integration/JCacheLoaderAdapter.java b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/integration/JCacheLoaderAdapter.java
index 9d11aec47d..560b96d410 100644
--- a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/integration/JCacheLoaderAdapter.java
+++ b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/integration/JCacheLoaderAdapter.java
@@ -29,7 +29,7 @@
 import javax.cache.integration.CacheLoader;
 import javax.cache.integration.CacheLoaderException;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.Ticker;
 import com.github.benmanes.caffeine.jcache.CacheProxy;
diff --git a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/integration/package-info.java b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/integration/package-info.java
index 2ee221290d..960a1d344c 100644
--- a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/integration/package-info.java
+++ b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/integration/package-info.java
@@ -1,11 +1,7 @@
+@NullMarked
 @CheckReturnValue
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.FIELD)
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.PARAMETER)
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.RETURN)
 package com.github.benmanes.caffeine.jcache.integration;
 
-import org.checkerframework.checker.nullness.qual.NonNull;
-import org.checkerframework.framework.qual.DefaultQualifier;
-import org.checkerframework.framework.qual.TypeUseLocation;
+import org.jspecify.annotations.NullMarked;
 
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/management/JCacheStatisticsMXBean.java b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/management/JCacheStatisticsMXBean.java
index 859dbc36fd..509cd82e49 100644
--- a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/management/JCacheStatisticsMXBean.java
+++ b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/management/JCacheStatisticsMXBean.java
@@ -20,8 +20,6 @@
 
 import javax.cache.management.CacheStatisticsMXBean;
 
-import org.checkerframework.checker.index.qual.NonNegative;
-
 /**
  * Caffeine JCache statistics.
  *
@@ -82,7 +80,7 @@ public float getCacheHitPercentage() {
    *
    * @param count the number of hits to record
    */
-  public void recordHits(@NonNegative long count) {
+  public void recordHits(long count) {
     if (enabled) {
       hits.add(count);
     }
@@ -105,7 +103,7 @@ public float getCacheMissPercentage() {
    *
    * @param count the number of misses to record
    */
-  public void recordMisses(@NonNegative long count) {
+  public void recordMisses(long count) {
     if (enabled) {
       misses.add(count);
     }
@@ -126,7 +124,7 @@ public long getCachePuts() {
    *
    * @param count the number of writes to record
    */
-  public void recordPuts(@NonNegative long count) {
+  public void recordPuts(long count) {
     if (enabled && (count != 0)) {
       puts.add(count);
     }
@@ -142,7 +140,7 @@ public long getCacheRemovals() {
    *
    * @param count the number of removals to record
    */
-  public void recordRemovals(@NonNegative long count) {
+  public void recordRemovals(long count) {
     if (enabled) {
       removals.add(count);
     }
@@ -158,7 +156,7 @@ public long getCacheEvictions() {
    *
    * @param count the number of evictions to record
    */
-  public void recordEvictions(@NonNegative long count) {
+  public void recordEvictions(long count) {
     if (enabled) {
       evictions.add(count);
     }
diff --git a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/management/package-info.java b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/management/package-info.java
index 924b882947..bfa9b9e354 100644
--- a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/management/package-info.java
+++ b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/management/package-info.java
@@ -1,11 +1,7 @@
+@NullMarked
 @CheckReturnValue
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.FIELD)
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.PARAMETER)
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.RETURN)
 package com.github.benmanes.caffeine.jcache.management;
 
-import org.checkerframework.checker.nullness.qual.NonNull;
-import org.checkerframework.framework.qual.DefaultQualifier;
-import org.checkerframework.framework.qual.TypeUseLocation;
+import org.jspecify.annotations.NullMarked;
 
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/package-info.java b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/package-info.java
index 2e5866b425..a9077d3890 100644
--- a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/package-info.java
+++ b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/package-info.java
@@ -1,11 +1,7 @@
+@NullMarked
 @CheckReturnValue
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.FIELD)
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.PARAMETER)
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.RETURN)
 package com.github.benmanes.caffeine.jcache;
 
-import org.checkerframework.checker.nullness.qual.NonNull;
-import org.checkerframework.framework.qual.DefaultQualifier;
-import org.checkerframework.framework.qual.TypeUseLocation;
+import org.jspecify.annotations.NullMarked;
 
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/processor/EntryProcessorEntry.java b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/processor/EntryProcessorEntry.java
index 8c2639740f..cc937f8b24 100644
--- a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/processor/EntryProcessorEntry.java
+++ b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/processor/EntryProcessorEntry.java
@@ -23,7 +23,7 @@
 import javax.cache.processor.EntryProcessor;
 import javax.cache.processor.MutableEntry;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 /**
  * An entry that is consumed by an {@link EntryProcessor}. The updates to the entry are replayed
diff --git a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/processor/package-info.java b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/processor/package-info.java
index 784bafab93..d9612b40ab 100644
--- a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/processor/package-info.java
+++ b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/processor/package-info.java
@@ -1,11 +1,7 @@
+@NullMarked
 @CheckReturnValue
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.FIELD)
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.PARAMETER)
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.RETURN)
 package com.github.benmanes.caffeine.jcache.processor;
 
-import org.checkerframework.checker.nullness.qual.NonNull;
-import org.checkerframework.framework.qual.DefaultQualifier;
-import org.checkerframework.framework.qual.TypeUseLocation;
+import org.jspecify.annotations.NullMarked;
 
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/spi/CaffeineCachingProvider.java b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/spi/CaffeineCachingProvider.java
index bded9d9226..e64febf4f4 100644
--- a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/spi/CaffeineCachingProvider.java
+++ b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/spi/CaffeineCachingProvider.java
@@ -33,7 +33,7 @@
 import javax.cache.configuration.OptionalFeature;
 import javax.cache.spi.CachingProvider;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 import org.osgi.service.component.annotations.Activate;
 import org.osgi.service.component.annotations.Component;
 
diff --git a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/spi/package-info.java b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/spi/package-info.java
index 3cda819cd5..dbf49aa509 100644
--- a/jcache/src/main/java/com/github/benmanes/caffeine/jcache/spi/package-info.java
+++ b/jcache/src/main/java/com/github/benmanes/caffeine/jcache/spi/package-info.java
@@ -1,11 +1,7 @@
+@NullMarked
 @CheckReturnValue
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.FIELD)
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.PARAMETER)
-@DefaultQualifier(value = NonNull.class, locations = TypeUseLocation.RETURN)
 package com.github.benmanes.caffeine.jcache.spi;
 
-import org.checkerframework.checker.nullness.qual.NonNull;
-import org.checkerframework.framework.qual.DefaultQualifier;
-import org.checkerframework.framework.qual.TypeUseLocation;
+import org.jspecify.annotations.NullMarked;
 
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/jcache/src/test/java/com/github/benmanes/caffeine/jcache/AbstractJCacheTest.java b/jcache/src/test/java/com/github/benmanes/caffeine/jcache/AbstractJCacheTest.java
index 4f6871b333..59be4f1c5c 100644
--- a/jcache/src/test/java/com/github/benmanes/caffeine/jcache/AbstractJCacheTest.java
+++ b/jcache/src/test/java/com/github/benmanes/caffeine/jcache/AbstractJCacheTest.java
@@ -24,7 +24,7 @@
 import javax.cache.integration.CacheLoader;
 import javax.cache.spi.CachingProvider;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 import org.testng.annotations.AfterClass;
 import org.testng.annotations.AfterMethod;
 import org.testng.annotations.BeforeClass;
diff --git a/jcache/src/test/java/com/github/benmanes/caffeine/jcache/configuration/package-info.java b/jcache/src/test/java/com/github/benmanes/caffeine/jcache/configuration/package-info.java
index 37d466184a..d45ee11a63 100644
--- a/jcache/src/test/java/com/github/benmanes/caffeine/jcache/configuration/package-info.java
+++ b/jcache/src/test/java/com/github/benmanes/caffeine/jcache/configuration/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.jcache.configuration;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/jcache/src/test/java/com/github/benmanes/caffeine/jcache/copy/package-info.java b/jcache/src/test/java/com/github/benmanes/caffeine/jcache/copy/package-info.java
index 4b6aad596e..5aa6b49a90 100644
--- a/jcache/src/test/java/com/github/benmanes/caffeine/jcache/copy/package-info.java
+++ b/jcache/src/test/java/com/github/benmanes/caffeine/jcache/copy/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.jcache.copy;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/jcache/src/test/java/com/github/benmanes/caffeine/jcache/event/package-info.java b/jcache/src/test/java/com/github/benmanes/caffeine/jcache/event/package-info.java
index 9b3c6707d8..cd52195a6f 100644
--- a/jcache/src/test/java/com/github/benmanes/caffeine/jcache/event/package-info.java
+++ b/jcache/src/test/java/com/github/benmanes/caffeine/jcache/event/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.jcache.event;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/jcache/src/test/java/com/github/benmanes/caffeine/jcache/expiry/package-info.java b/jcache/src/test/java/com/github/benmanes/caffeine/jcache/expiry/package-info.java
index 31d27656a9..9370bdeb3a 100644
--- a/jcache/src/test/java/com/github/benmanes/caffeine/jcache/expiry/package-info.java
+++ b/jcache/src/test/java/com/github/benmanes/caffeine/jcache/expiry/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.jcache.expiry;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/jcache/src/test/java/com/github/benmanes/caffeine/jcache/integration/package-info.java b/jcache/src/test/java/com/github/benmanes/caffeine/jcache/integration/package-info.java
index 785bbd147e..960a1d344c 100644
--- a/jcache/src/test/java/com/github/benmanes/caffeine/jcache/integration/package-info.java
+++ b/jcache/src/test/java/com/github/benmanes/caffeine/jcache/integration/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.jcache.integration;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/jcache/src/test/java/com/github/benmanes/caffeine/jcache/issues/package-info.java b/jcache/src/test/java/com/github/benmanes/caffeine/jcache/issues/package-info.java
new file mode 100644
index 0000000000..59d7faccc7
--- /dev/null
+++ b/jcache/src/test/java/com/github/benmanes/caffeine/jcache/issues/package-info.java
@@ -0,0 +1,7 @@
+@NullMarked
+@CheckReturnValue
+package com.github.benmanes.caffeine.jcache.issues;
+
+import org.jspecify.annotations.NullMarked;
+
+import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/jcache/src/test/java/com/github/benmanes/caffeine/jcache/management/package-info.java b/jcache/src/test/java/com/github/benmanes/caffeine/jcache/management/package-info.java
index d3d6c07883..bfa9b9e354 100644
--- a/jcache/src/test/java/com/github/benmanes/caffeine/jcache/management/package-info.java
+++ b/jcache/src/test/java/com/github/benmanes/caffeine/jcache/management/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.jcache.management;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/jcache/src/test/java/com/github/benmanes/caffeine/jcache/package-info.java b/jcache/src/test/java/com/github/benmanes/caffeine/jcache/package-info.java
index cfeead53ba..a9077d3890 100644
--- a/jcache/src/test/java/com/github/benmanes/caffeine/jcache/package-info.java
+++ b/jcache/src/test/java/com/github/benmanes/caffeine/jcache/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.jcache;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/jcache/src/test/java/com/github/benmanes/caffeine/jcache/processor/package-info.java b/jcache/src/test/java/com/github/benmanes/caffeine/jcache/processor/package-info.java
index 59e0c1b095..d9612b40ab 100644
--- a/jcache/src/test/java/com/github/benmanes/caffeine/jcache/processor/package-info.java
+++ b/jcache/src/test/java/com/github/benmanes/caffeine/jcache/processor/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.jcache.processor;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/jcache/src/test/java/com/github/benmanes/caffeine/jcache/size/package-info.java b/jcache/src/test/java/com/github/benmanes/caffeine/jcache/size/package-info.java
index 9bddc5d7f6..72cf354b38 100644
--- a/jcache/src/test/java/com/github/benmanes/caffeine/jcache/size/package-info.java
+++ b/jcache/src/test/java/com/github/benmanes/caffeine/jcache/size/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.jcache.size;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/jcache/src/test/java/com/github/benmanes/caffeine/jcache/spi/package-info.java b/jcache/src/test/java/com/github/benmanes/caffeine/jcache/spi/package-info.java
index dcaba8edba..dbf49aa509 100644
--- a/jcache/src/test/java/com/github/benmanes/caffeine/jcache/spi/package-info.java
+++ b/jcache/src/test/java/com/github/benmanes/caffeine/jcache/spi/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.jcache.spi;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/BasicSettings.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/BasicSettings.java
index c300e38488..06b2ca9421 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/BasicSettings.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/BasicSettings.java
@@ -26,7 +26,7 @@
 import java.util.function.Function;
 import java.util.regex.Pattern;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.simulator.admission.Admission;
 import com.github.benmanes.caffeine.cache.simulator.membership.FilterType;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/clairvoyant/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/clairvoyant/package-info.java
new file mode 100644
index 0000000000..6f6fa07b64
--- /dev/null
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/clairvoyant/package-info.java
@@ -0,0 +1,7 @@
+@NullMarked
+@CheckReturnValue
+package com.github.benmanes.caffeine.cache.simulator.admission.clairvoyant;
+
+import org.jspecify.annotations.NullMarked;
+
+import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/countmin4/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/countmin4/package-info.java
index 29a5355fe0..3ffc1de122 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/countmin4/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/countmin4/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.admission.countmin4;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/countmin64/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/countmin64/package-info.java
index 2ae76e82fa..9defe7312b 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/countmin64/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/countmin64/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.admission.countmin64;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/package-info.java
index 973e4d0881..46bb5dbaee 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.admission;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/perfect/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/perfect/package-info.java
index 11990c5a01..bbc14a00e5 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/perfect/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/perfect/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.admission.perfect;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/table/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/table/package-info.java
index 91c5f05966..13cb90aff6 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/table/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/table/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.admission.table;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/tinycache/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/tinycache/package-info.java
index 566830198b..92fffac8ff 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/tinycache/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/tinycache/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.admission.tinycache;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/membership/bloom/BloomFilter.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/membership/bloom/BloomFilter.java
index 58a646162a..1cff5bf352 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/membership/bloom/BloomFilter.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/membership/bloom/BloomFilter.java
@@ -19,8 +19,6 @@
 
 import java.util.Arrays;
 
-import org.checkerframework.checker.index.qual.NonNegative;
-
 import com.github.benmanes.caffeine.cache.simulator.BasicSettings;
 import com.github.benmanes.caffeine.cache.simulator.membership.Membership;
 import com.google.errorprone.annotations.Var;
@@ -68,7 +66,7 @@ public BloomFilter(Config config) {
    * @param fpp the false positive probability, where {@literal 0.0 > fpp < 1.0}
    */
   @SuppressWarnings("Varifier")
-  public void ensureCapacity(@NonNegative long expectedInsertions, @NonNegative double fpp) {
+  public void ensureCapacity(long expectedInsertions, double fpp) {
     checkArgument(expectedInsertions >= 0);
     checkArgument(fpp > 0 && fpp < 1);
 
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/membership/bloom/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/membership/bloom/package-info.java
index 114cb94d84..4ad210fe4f 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/membership/bloom/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/membership/bloom/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.membership.bloom;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/membership/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/membership/package-info.java
index 25efd6de8c..f144e9ae8e 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/membership/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/membership/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.membership;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/package-info.java
index ccf25988e9..254ed24d9a 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/AbstractTraceReader.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/AbstractTraceReader.java
index 24fb97216c..f14fe70de2 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/AbstractTraceReader.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/AbstractTraceReader.java
@@ -34,7 +34,7 @@
 import org.apache.commons.compress.compressors.CompressorException;
 import org.apache.commons.compress.compressors.CompressorStreamFactory;
 import org.apache.commons.io.input.CloseShieldInputStream;
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 import org.tukaani.xz.XZInputStream;
 
 import com.google.common.base.Throwables;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/adapt_size/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/adapt_size/package-info.java
index a9927b38e0..7dc6bbee82 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/adapt_size/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/adapt_size/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.parser.adapt_size;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/address/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/address/package-info.java
index 2883ffdf43..64b95f65ce 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/address/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/address/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.parser.address;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/address/penalties/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/address/penalties/package-info.java
index 39c149fec8..3c3aa40a21 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/address/penalties/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/address/penalties/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.parser.address.penalties;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/arc/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/arc/package-info.java
index 1b78db9d65..d4f0752741 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/arc/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/arc/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.parser.arc;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/baleen/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/baleen/package-info.java
index 4aba96f214..57293c18b0 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/baleen/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/baleen/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.parser.baleen;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/cache2k/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/cache2k/package-info.java
index d0822ce85a..857908ae08 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/cache2k/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/cache2k/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.parser.cache2k;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/cachelib/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/cachelib/package-info.java
index 2b48c98a10..0e1659eb87 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/cachelib/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/cachelib/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.parser.cachelib;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/camelab/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/camelab/package-info.java
index 944c709600..8995efc422 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/camelab/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/camelab/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.parser.camelab;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/cloud_physics/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/cloud_physics/package-info.java
index c92e6906e0..7961c1af4c 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/cloud_physics/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/cloud_physics/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.parser.cloud_physics;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/corda/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/corda/package-info.java
index 250868eb9d..66217ad508 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/corda/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/corda/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.parser.corda;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/glcache/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/glcache/package-info.java
index 8727e2f92f..41f33da682 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/glcache/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/glcache/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.parser.glcache;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/gradle/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/gradle/package-info.java
index 516488930f..bbe39383da 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/gradle/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/gradle/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.parser.gradle;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/kaggle/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/kaggle/package-info.java
index f2480baca1..6eb691e033 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/kaggle/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/kaggle/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.parser.kaggle;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/libcachesim/csv/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/libcachesim/csv/package-info.java
index c3ee916633..247b8ead68 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/libcachesim/csv/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/libcachesim/csv/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.parser.libcachesim.csv;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/libcachesim/twitter/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/libcachesim/twitter/package-info.java
index 2d6ff32c80..538926f988 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/libcachesim/twitter/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/libcachesim/twitter/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.parser.libcachesim.twitter;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/lirs/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/lirs/package-info.java
index 35a6d42362..bca5169f38 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/lirs/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/lirs/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.parser.lirs;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/lrb/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/lrb/package-info.java
index c9f6bcc61a..c7da3d502e 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/lrb/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/lrb/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.parser.lrb;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/package-info.java
index 44b4dd0eea..c4185a7386 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.parser;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/scarab/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/scarab/package-info.java
index 3c3a4b78e3..f7d182dad7 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/scarab/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/scarab/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.parser.scarab;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/snia/cambridge/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/snia/cambridge/package-info.java
index 32fb572e7f..56b257a09a 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/snia/cambridge/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/snia/cambridge/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.parser.snia.cambridge;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/snia/enterprise/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/snia/enterprise/package-info.java
index aa18824326..ee192436e5 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/snia/enterprise/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/snia/enterprise/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.parser.snia.enterprise;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/snia/keyvalue/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/snia/keyvalue/package-info.java
index 600dc967b3..65de42328f 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/snia/keyvalue/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/snia/keyvalue/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.parser.snia.keyvalue;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/snia/parallel/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/snia/parallel/package-info.java
index b537cc9881..fd73ae6080 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/snia/parallel/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/snia/parallel/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.parser.snia.parallel;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/snia/systor/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/snia/systor/package-info.java
index 6b9a72fa41..27456209fd 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/snia/systor/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/snia/systor/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.parser.snia.systor;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/tragen/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/tragen/package-info.java
index 732b965246..c40c1a47d0 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/tragen/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/tragen/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.parser.tragen;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/twitter/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/twitter/package-info.java
index 37d9812b67..671bfbb3ac 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/twitter/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/twitter/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.parser.twitter;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/umass/network/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/umass/network/package-info.java
index 3edda359fe..6d483f8b66 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/umass/network/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/umass/network/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.parser.umass.network;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/umass/storage/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/umass/storage/package-info.java
index 425ab334b0..da705d4dd6 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/umass/storage/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/umass/storage/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.parser.umass.storage;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/wikipedia/WikipediaTraceReader.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/wikipedia/WikipediaTraceReader.java
index d9ddf1ad58..5842cbbe8e 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/wikipedia/WikipediaTraceReader.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/wikipedia/WikipediaTraceReader.java
@@ -19,7 +19,7 @@
 import java.util.stream.LongStream;
 
 import org.apache.commons.lang3.StringUtils;
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.simulator.parser.TextTraceReader;
 import com.github.benmanes.caffeine.cache.simulator.parser.TraceReader.KeyOnlyTraceReader;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/wikipedia/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/wikipedia/package-info.java
index ce0b5ce205..76905c2fa0 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/wikipedia/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/parser/wikipedia/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.parser.wikipedia;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/AccessEvent.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/AccessEvent.java
index 204105ee07..70922f213e 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/AccessEvent.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/AccessEvent.java
@@ -19,6 +19,8 @@
 
 import java.util.Objects;
 
+import org.jspecify.annotations.Nullable;
+
 import com.google.common.base.MoreObjects;
 import com.google.errorprone.annotations.Immutable;
 
@@ -61,7 +63,7 @@ public boolean isPenaltyAware() {
   }
 
   @Override
-  public boolean equals(Object o) {
+  public boolean equals(@Nullable Object o) {
     if (o == this) {
       return true;
     } else if (!(o instanceof AccessEvent)) {
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/PolicyActor.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/PolicyActor.java
index 428d3da9b6..97a112136e 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/PolicyActor.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/PolicyActor.java
@@ -21,6 +21,8 @@
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.Semaphore;
 
+import org.jspecify.annotations.Nullable;
+
 import com.github.benmanes.caffeine.cache.simulator.BasicSettings;
 import com.google.common.collect.ImmutableList;
 
@@ -30,12 +32,12 @@
  * @author ben.manes@gmail.com (Ben Manes)
  */
 public final class PolicyActor {
-  private final CompletableFuture<Void> completed;
+  private final CompletableFuture<@Nullable Void> completed;
   private final Semaphore semaphore;
   private final Policy policy;
   private final Thread parent;
 
-  private CompletableFuture<Void> future;
+  private CompletableFuture<@Nullable Void> future;
 
   /**
    * Creates an actor that executes the policy actions asynchronously over a buffered channel.
@@ -63,7 +65,7 @@ public void finish() {
   }
 
   /** Return the future that signals the policy's completion. */
-  public CompletableFuture<Void> completed() {
+  public CompletableFuture<@Nullable Void> completed() {
     return completed;
   }
 
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/adaptive/ArcPolicy.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/adaptive/ArcPolicy.java
index a036b847ae..134395ba03 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/adaptive/ArcPolicy.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/adaptive/ArcPolicy.java
@@ -17,7 +17,7 @@
 
 import static com.google.common.base.Preconditions.checkState;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.simulator.BasicSettings;
 import com.github.benmanes.caffeine.cache.simulator.policy.Policy.KeyOnlyPolicy;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/adaptive/CarPolicy.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/adaptive/CarPolicy.java
index c002e9291f..7361fc94b2 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/adaptive/CarPolicy.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/adaptive/CarPolicy.java
@@ -17,7 +17,7 @@
 
 import static com.google.common.base.Preconditions.checkState;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.simulator.BasicSettings;
 import com.github.benmanes.caffeine.cache.simulator.policy.Policy.KeyOnlyPolicy;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/adaptive/CartPolicy.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/adaptive/CartPolicy.java
index a3841074a7..c459e217ef 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/adaptive/CartPolicy.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/adaptive/CartPolicy.java
@@ -17,7 +17,7 @@
 
 import static com.google.common.base.Preconditions.checkState;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.simulator.BasicSettings;
 import com.github.benmanes.caffeine.cache.simulator.policy.Policy.KeyOnlyPolicy;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/adaptive/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/adaptive/package-info.java
index 9dcd7bc606..f4b65d2e4b 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/adaptive/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/adaptive/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.policy.adaptive;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/greedy_dual/CampPolicy.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/greedy_dual/CampPolicy.java
index eccfde2cba..587830ba25 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/greedy_dual/CampPolicy.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/greedy_dual/CampPolicy.java
@@ -22,7 +22,7 @@
 import java.util.Objects;
 import java.util.TreeSet;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.simulator.BasicSettings;
 import com.github.benmanes.caffeine.cache.simulator.policy.AccessEvent;
@@ -218,7 +218,7 @@ public int compareTo(Sentinel sentinel) {
     }
 
     @Override
-    public boolean equals(Object o) {
+    public boolean equals(@Nullable Object o) {
       if (this == o) {
         return true;
       } else if (!(o instanceof Sentinel)) {
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/greedy_dual/GDWheelPolicy.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/greedy_dual/GDWheelPolicy.java
index a593aac63f..01079c4cc5 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/greedy_dual/GDWheelPolicy.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/greedy_dual/GDWheelPolicy.java
@@ -18,7 +18,7 @@
 import static com.github.benmanes.caffeine.cache.simulator.policy.Policy.Characteristic.WEIGHTED;
 import static com.google.common.base.Preconditions.checkState;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.simulator.BasicSettings;
 import com.github.benmanes.caffeine.cache.simulator.policy.AccessEvent;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/greedy_dual/GdsfPolicy.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/greedy_dual/GdsfPolicy.java
index af83c3a7df..f46b61a899 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/greedy_dual/GdsfPolicy.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/greedy_dual/GdsfPolicy.java
@@ -23,6 +23,8 @@
 import java.util.Set;
 import java.util.TreeSet;
 
+import org.jspecify.annotations.Nullable;
+
 import com.github.benmanes.caffeine.cache.simulator.BasicSettings;
 import com.github.benmanes.caffeine.cache.simulator.policy.AccessEvent;
 import com.github.benmanes.caffeine.cache.simulator.policy.Policy;
@@ -204,7 +206,7 @@ public int compareTo(Node node) {
     }
 
     @Override
-    public boolean equals(Object o) {
+    public boolean equals(@Nullable Object o) {
       if (o == this) {
         return true;
       } else if (!(o instanceof Node)) {
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/greedy_dual/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/greedy_dual/package-info.java
index 9044c5264d..7e18b55d04 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/greedy_dual/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/greedy_dual/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.policy.greedy_dual;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/ClockProPlusPolicy.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/ClockProPlusPolicy.java
index ed5d80053f..e684a0ae14 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/ClockProPlusPolicy.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/ClockProPlusPolicy.java
@@ -17,7 +17,7 @@
 
 import static com.google.common.base.Preconditions.checkState;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.simulator.BasicSettings;
 import com.github.benmanes.caffeine.cache.simulator.policy.Policy.KeyOnlyPolicy;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/ClockProPolicy.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/ClockProPolicy.java
index 04dca61b91..b57aee8620 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/ClockProPolicy.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/ClockProPolicy.java
@@ -17,7 +17,7 @@
 
 import static com.google.common.base.Preconditions.checkState;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.simulator.BasicSettings;
 import com.github.benmanes.caffeine.cache.simulator.policy.Policy.KeyOnlyPolicy;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/DClockPolicy.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/DClockPolicy.java
index 22ae3cd117..d5309d5df2 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/DClockPolicy.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/DClockPolicy.java
@@ -22,7 +22,7 @@
 import java.util.List;
 import java.util.Set;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.simulator.BasicSettings;
 import com.github.benmanes.caffeine.cache.simulator.policy.Policy;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/FrdPolicy.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/FrdPolicy.java
index 28118dae60..9be61f96ee 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/FrdPolicy.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/FrdPolicy.java
@@ -17,7 +17,7 @@
 
 import static com.google.common.base.Preconditions.checkState;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.simulator.BasicSettings;
 import com.github.benmanes.caffeine.cache.simulator.policy.Policy.KeyOnlyPolicy;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/HillClimberFrdPolicy.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/HillClimberFrdPolicy.java
index 2a5a5ca4ae..087ffb3ae3 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/HillClimberFrdPolicy.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/HillClimberFrdPolicy.java
@@ -17,7 +17,7 @@
 
 import static com.google.common.base.Preconditions.checkState;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.simulator.BasicSettings;
 import com.github.benmanes.caffeine.cache.simulator.policy.Policy.KeyOnlyPolicy;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/IndicatorFrdPolicy.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/IndicatorFrdPolicy.java
index a33f5ceb56..c1d829fc5c 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/IndicatorFrdPolicy.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/IndicatorFrdPolicy.java
@@ -17,7 +17,7 @@
 
 import static com.google.common.base.Preconditions.checkState;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.simulator.BasicSettings;
 import com.github.benmanes.caffeine.cache.simulator.policy.Policy.KeyOnlyPolicy;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/LirsPolicy.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/LirsPolicy.java
index 18e7be7127..38d52c5b8f 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/LirsPolicy.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/LirsPolicy.java
@@ -20,7 +20,7 @@
 import java.util.ArrayList;
 import java.util.List;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.simulator.BasicSettings;
 import com.github.benmanes.caffeine.cache.simulator.policy.Policy.KeyOnlyPolicy;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/package-info.java
index 5c1f5dec6c..cd27df88b4 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/irr/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.policy.irr;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/linked/FrequentlyUsedPolicy.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/linked/FrequentlyUsedPolicy.java
index 202d62caa9..149a1c5d73 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/linked/FrequentlyUsedPolicy.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/linked/FrequentlyUsedPolicy.java
@@ -22,7 +22,7 @@
 import java.util.Set;
 
 import org.apache.commons.lang3.StringUtils;
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.simulator.BasicSettings;
 import com.github.benmanes.caffeine.cache.simulator.admission.Admission;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/linked/LinkedPolicy.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/linked/LinkedPolicy.java
index 1d4423b554..b801d0a630 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/linked/LinkedPolicy.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/linked/LinkedPolicy.java
@@ -22,7 +22,7 @@
 import java.util.Set;
 
 import org.apache.commons.lang3.StringUtils;
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.simulator.BasicSettings;
 import com.github.benmanes.caffeine.cache.simulator.admission.Admission;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/linked/MultiQueuePolicy.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/linked/MultiQueuePolicy.java
index da09e306aa..945bdc06d3 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/linked/MultiQueuePolicy.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/linked/MultiQueuePolicy.java
@@ -19,7 +19,7 @@
 
 import java.util.Arrays;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.simulator.BasicSettings;
 import com.github.benmanes.caffeine.cache.simulator.policy.Policy.KeyOnlyPolicy;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/linked/S4LruPolicy.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/linked/S4LruPolicy.java
index b69adba496..8d4da717ab 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/linked/S4LruPolicy.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/linked/S4LruPolicy.java
@@ -21,7 +21,7 @@
 import java.util.Arrays;
 import java.util.Set;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.simulator.BasicSettings;
 import com.github.benmanes.caffeine.cache.simulator.admission.Admission;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/linked/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/linked/package-info.java
index 3eb8cba267..7444af06a8 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/linked/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/linked/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.policy.linked;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/opt/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/opt/package-info.java
index 334c9e3a68..fac924fb6a 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/opt/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/opt/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.policy.opt;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/package-info.java
index c9b2a6974a..55fb513cea 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.policy;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/product/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/product/package-info.java
index 0a5e777d6f..51ecf285f7 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/product/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/product/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.policy.product;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sampled/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sampled/package-info.java
index d0993888d2..fdb33401ef 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sampled/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sampled/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.policy.sampled;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/WindowTinyLfuPolicy.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/WindowTinyLfuPolicy.java
index a96b5914a8..96d728cfaf 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/WindowTinyLfuPolicy.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/WindowTinyLfuPolicy.java
@@ -21,7 +21,7 @@
 import java.util.List;
 import java.util.Set;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.simulator.BasicSettings;
 import com.github.benmanes.caffeine.cache.simulator.admission.Admission;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/climbing/HillClimberWindowTinyLfuPolicy.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/climbing/HillClimberWindowTinyLfuPolicy.java
index 0a7c760a9c..f8be96c951 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/climbing/HillClimberWindowTinyLfuPolicy.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/climbing/HillClimberWindowTinyLfuPolicy.java
@@ -28,7 +28,7 @@
 import java.util.List;
 import java.util.Set;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.simulator.BasicSettings;
 import com.github.benmanes.caffeine.cache.simulator.admission.Admission;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/climbing/gradient/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/climbing/gradient/package-info.java
index 8d78ebb0ed..6880da9141 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/climbing/gradient/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/climbing/gradient/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.policy.sketch.climbing.gradient;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/climbing/hill/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/climbing/hill/package-info.java
index 9b128a21f5..a86bc21321 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/climbing/hill/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/climbing/hill/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.policy.sketch.climbing.hill;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/climbing/inference/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/climbing/inference/package-info.java
index f84a278b5f..1cb926a6da 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/climbing/inference/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/climbing/inference/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.policy.sketch.climbing.inference;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/climbing/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/climbing/package-info.java
index b0d70d138f..dc7b3b4abc 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/climbing/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/climbing/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.policy.sketch.climbing;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/climbing/sim/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/climbing/sim/package-info.java
index 04af759b70..93f6ea29cb 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/climbing/sim/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/climbing/sim/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.policy.sketch.climbing.sim;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/feedback/FeedbackTinyLfuPolicy.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/feedback/FeedbackTinyLfuPolicy.java
index 34d2e34c76..02623a2b77 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/feedback/FeedbackTinyLfuPolicy.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/feedback/FeedbackTinyLfuPolicy.java
@@ -19,7 +19,7 @@
 
 import java.util.Map;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.simulator.BasicSettings;
 import com.github.benmanes.caffeine.cache.simulator.admission.Admission;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/feedback/FeedbackWindowTinyLfuPolicy.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/feedback/FeedbackWindowTinyLfuPolicy.java
index 4a99714b24..310044509e 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/feedback/FeedbackWindowTinyLfuPolicy.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/feedback/FeedbackWindowTinyLfuPolicy.java
@@ -23,7 +23,7 @@
 import java.util.Map;
 import java.util.Set;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.simulator.BasicSettings;
 import com.github.benmanes.caffeine.cache.simulator.admission.Admission;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/feedback/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/feedback/package-info.java
index 7c607901db..5a0d3ceb9d 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/feedback/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/feedback/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.policy.sketch.feedback;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/package-info.java
index 2a1bec52d5..766fe3d97a 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.policy.sketch;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/segment/FullySegmentedWindowTinyLfuPolicy.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/segment/FullySegmentedWindowTinyLfuPolicy.java
index 532a942b97..cab36c130c 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/segment/FullySegmentedWindowTinyLfuPolicy.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/segment/FullySegmentedWindowTinyLfuPolicy.java
@@ -21,7 +21,7 @@
 import java.util.List;
 import java.util.Set;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.simulator.BasicSettings;
 import com.github.benmanes.caffeine.cache.simulator.admission.Admission;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/segment/LruWindowTinyLfuPolicy.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/segment/LruWindowTinyLfuPolicy.java
index 8d11d526bd..d21f5eb9b5 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/segment/LruWindowTinyLfuPolicy.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/segment/LruWindowTinyLfuPolicy.java
@@ -21,7 +21,7 @@
 import java.util.List;
 import java.util.Set;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.simulator.BasicSettings;
 import com.github.benmanes.caffeine.cache.simulator.admission.Admission;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/segment/S4WindowTinyLfuPolicy.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/segment/S4WindowTinyLfuPolicy.java
index 3aab28286d..9cfa54db45 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/segment/S4WindowTinyLfuPolicy.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/segment/S4WindowTinyLfuPolicy.java
@@ -22,7 +22,7 @@
 import java.util.List;
 import java.util.Set;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.simulator.BasicSettings;
 import com.github.benmanes.caffeine.cache.simulator.admission.Admission;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/segment/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/segment/package-info.java
index 007fbd2a50..ed38a397d8 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/segment/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/segment/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.policy.sketch.segment;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/tinycache/WindowTinyCachePolicy.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/tinycache/WindowTinyCachePolicy.java
index 4dcf451810..b939dc7def 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/tinycache/WindowTinyCachePolicy.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/tinycache/WindowTinyCachePolicy.java
@@ -15,7 +15,7 @@
  */
 package com.github.benmanes.caffeine.cache.simulator.policy.sketch.tinycache;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.simulator.BasicSettings;
 import com.github.benmanes.caffeine.cache.simulator.admission.tinycache.TinyCache;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/tinycache/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/tinycache/package-info.java
index 6923e34859..f3bc67a50c 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/tinycache/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/sketch/tinycache/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.policy.sketch.tinycache;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/two_queue/S3FifoPolicy.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/two_queue/S3FifoPolicy.java
index cc424dff84..4d02ad3607 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/two_queue/S3FifoPolicy.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/two_queue/S3FifoPolicy.java
@@ -21,7 +21,7 @@
 import java.util.LinkedHashSet;
 import java.util.function.IntConsumer;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.simulator.BasicSettings;
 import com.github.benmanes.caffeine.cache.simulator.policy.AccessEvent;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/two_queue/TuQueuePolicy.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/two_queue/TuQueuePolicy.java
index cda39edd49..481febfb95 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/two_queue/TuQueuePolicy.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/two_queue/TuQueuePolicy.java
@@ -17,7 +17,7 @@
 
 import static com.google.common.base.Preconditions.checkState;
 
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import com.github.benmanes.caffeine.cache.simulator.BasicSettings;
 import com.github.benmanes.caffeine.cache.simulator.policy.Policy.KeyOnlyPolicy;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/two_queue/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/two_queue/package-info.java
index 0cecb81a77..1e0f50243e 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/two_queue/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/two_queue/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.policy.two_queue;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/report/csv/CombinedCsvReport.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/report/csv/CombinedCsvReport.java
index 329b76d5cd..89e793b7a3 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/report/csv/CombinedCsvReport.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/report/csv/CombinedCsvReport.java
@@ -26,6 +26,8 @@
 import java.util.TreeMap;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
+
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableSortedMap;
 import com.univocity.parsers.csv.CsvParser;
@@ -113,7 +115,7 @@ private static final class Label implements Comparable<Label> {
       this.size = size;
     }
     @Override
-    public boolean equals(Object o) {
+    public boolean equals(@Nullable Object o) {
       return (o instanceof Label) && (compareTo((Label) o) == 0);
     }
     @Override
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/report/csv/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/report/csv/package-info.java
index 8168806bea..b926df8ab8 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/report/csv/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/report/csv/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.report.csv;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/report/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/report/package-info.java
index a96d5dc155..58bd9339d0 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/report/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/report/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.report;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/report/table/package-info.java b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/report/table/package-info.java
index d5be48201b..6601ed170b 100644
--- a/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/report/table/package-info.java
+++ b/simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/report/table/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.report.table;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;
diff --git a/simulator/src/test/java/com/github/benmanes/caffeine/cache/simulator/admission/bloom/package-info.java b/simulator/src/test/java/com/github/benmanes/caffeine/cache/simulator/admission/bloom/package-info.java
index 26ded75d72..28e3aa8964 100644
--- a/simulator/src/test/java/com/github/benmanes/caffeine/cache/simulator/admission/bloom/package-info.java
+++ b/simulator/src/test/java/com/github/benmanes/caffeine/cache/simulator/admission/bloom/package-info.java
@@ -1,4 +1,7 @@
+@NullMarked
 @CheckReturnValue
 package com.github.benmanes.caffeine.cache.simulator.admission.bloom;
 
+import org.jspecify.annotations.NullMarked;
+
 import com.google.errorprone.annotations.CheckReturnValue;