BatchProgramModule: Don't bind event classes to null

Instead, bind them to the DISABLED instance.

Change-Id: I599caac02ae98800fba641c1e4f6088a9c894c48

gerrit-pgm/src/main/java/com/google/gerrit/pgm/util/BatchProgramModule.java

@@ -168,8 +168,8 @@ public class BatchProgramModule extends FactoryModule {
 
     bind(ChangeJson.Factory.class).toProvider(Providers.<ChangeJson.Factory>of(null));
     bind(EventUtil.class).toProvider(Providers.<EventUtil>of(null));
-    bind(GitReferenceUpdated.class).toProvider(Providers.<GitReferenceUpdated>of(null));
+    bind(GitReferenceUpdated.class).toInstance(GitReferenceUpdated.DISABLED);
-    bind(RevisionCreated.class).toProvider(Providers.<RevisionCreated>of(null));
+    bind(RevisionCreated.class).toInstance(RevisionCreated.DISABLED);
     bind(AccountVisibility.class).toProvider(AccountVisibilityProvider.class).in(SINGLETON);
   }
 }

gerrit-server/src/main/java/com/google/gerrit/server/extensions/events/RevisionCreated.java

@@ -37,6 +37,17 @@ import org.slf4j.LoggerFactory;
 public class RevisionCreated {
   private static final Logger log = LoggerFactory.getLogger(RevisionCreated.class);
 
+  public static final RevisionCreated DISABLED =
+      new RevisionCreated() {
+        @Override
+        public void fire(
+            Change change,
+            PatchSet patchSet,
+            Account uploader,
+            Timestamp when,
+            NotifyHandling notify) {}
+      };
+
   private final DynamicSet<RevisionCreatedListener> listeners;
   private final EventUtil util;
 
@@ -46,6 +57,11 @@ public class RevisionCreated {
     this.util = util;
   }
 
+  private RevisionCreated() {
+    this.listeners = null;
+    this.util = null;
+  }
+
   public void fire(
       Change change, PatchSet patchSet, Account uploader, Timestamp when, NotifyHandling notify) {
     if (!listeners.iterator().hasNext()) {