Update annotations in JCache code.

jcache/src/main/java/com/github/benmanes/caffeine/jcache/LoadingCacheProxy.java

@@ -52,7 +52,7 @@ public final class LoadingCacheProxy<K, V> extends CacheProxy<K, V> {
 
   @SuppressWarnings({"PMD.ExcessiveParameterList", "TooManyParameters"})
   public LoadingCacheProxy(String name, Executor executor, CacheManager cacheManager,
-      CaffeineConfiguration<K, V> configuration, LoadingCache<K, Expirable<V>> cache,
+      CaffeineConfiguration<K, V> configuration, LoadingCache<K, @Nullable Expirable<V>> cache,
       EventDispatcher<K, V> dispatcher, CacheLoader<K, V> cacheLoader,
       ExpiryPolicy expiry, Ticker ticker, JCacheStatisticsMXBean statistics) {
     super(name, executor, cacheManager, configuration, cache, dispatcher,

jcache/src/main/java/com/github/benmanes/caffeine/jcache/integration/JCacheLoaderAdapter.java

@@ -43,7 +43,7 @@
  * @author [email protected] (Ben Manes)
  */
 public final class JCacheLoaderAdapter<K, V>
-    implements com.github.benmanes.caffeine.cache.CacheLoader<K, Expirable<V>> {
+    implements com.github.benmanes.caffeine.cache.CacheLoader<K, @Nullable Expirable<V>> {
   private static final Logger logger = System.getLogger(JCacheLoaderAdapter.class.getName());
 
   private final JCacheStatisticsMXBean statistics;