Upgrade Error Prone 2.14.0 -> 2.15.0 (#179)

See:
- https://github.com/google/error-prone/releases/tag/v2.15.0
- google/error-prone@v2.14.0...v2.15.0
- PicnicSupermarket/error-prone@v2.14.0-picnic-2...v2.15.0-picnic-3

error-prone-contrib/pom.xml

@@ -138,6 +138,11 @@
             <artifactId>value-annotations</artifactId>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.jspecify</groupId>
+            <artifactId>jspecify</artifactId>
+            <scope>provided</scope>
+        </dependency>
         <dependency>
             <groupId>org.junit.jupiter</groupId>
             <artifactId>junit-jupiter-api</artifactId>

error-prone-contrib/src/main/java/tech/picnic/errorprone/refastertemplates/RxJava2AdapterTemplates.java

@@ -9,6 +9,7 @@
 import io.reactivex.Maybe;
 import io.reactivex.Observable;
 import io.reactivex.Single;
+import org.jspecify.nullness.Nullable;
 import reactor.adapter.rxjava.RxJava2Adapter;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
@@ -20,14 +21,14 @@ private RxJava2AdapterTemplates() {}
   /** Use the fluent API style when using {@link RxJava2Adapter#completableToMono}. */
   static final class CompletableToMono {
     @BeforeTemplate
-    Mono<Void> before(Completable completable) {
+    Mono<@Nullable Void> before(Completable completable) {
       return Refaster.anyOf(
           RxJava2Adapter.completableToMono(completable),
           completable.to(RxJava2Adapter::completableToMono));
     }
 
     @AfterTemplate
-    Mono<Void> after(Completable completable) {
+    Mono<@Nullable Void> after(Completable completable) {
       return completable.as(RxJava2Adapter::completableToMono);
     }
   }

error-prone-contrib/src/main/java/tech/picnic/errorprone/refastertemplates/StringTemplates.java

@@ -130,7 +130,7 @@ String after(Object object) {
    */
   // XXX: This template is analogous to `StringValueOf` above. Arguably this is its generalization.
   // If/when Refaster is extended to understand this, delete the template above.
-  static final class StringValueOfMethodReference<T> {
+  static final class StringValueOfMethodReference {
     @BeforeTemplate
     Function<Object, String> before() {
       return Objects::toString;

pom.xml

@@ -144,8 +144,8 @@
         <version.auto-service>1.0.1</version.auto-service>
         <version.auto-value>1.9</version.auto-value>
         <version.error-prone>${version.error-prone-orig}</version.error-prone>
-        <version.error-prone-fork>v${version.error-prone-orig}-picnic-2</version.error-prone-fork>
-        <version.error-prone-orig>2.14.0</version.error-prone-orig>
+        <version.error-prone-fork>v${version.error-prone-orig}-picnic-3</version.error-prone-fork>
+        <version.error-prone-orig>2.15.0</version.error-prone-orig>
         <version.error-prone-slf4j>0.1.15</version.error-prone-slf4j>
         <version.guava-beta-checker>1.0</version.guava-beta-checker>
         <version.jdk>11</version.jdk>
@@ -378,6 +378,11 @@
                 <artifactId>value-annotations</artifactId>
                 <version>2.9.2</version>
             </dependency>
+            <dependency>
+                <groupId>org.jspecify</groupId>
+                <artifactId>jspecify</artifactId>
+                <version>0.2.0</version>
+            </dependency>
             <dependency>
                 <groupId>org.junit</groupId>
                 <artifactId>junit-bom</artifactId>