[findbugs] equals() must return false for null argument

The contract defined by java.lang.Object.equals() requires that it
must return false if passed a null argument.

Change-Id: I0b54beeeaed7fbd87d7e3ea5c4d4f5ae3c7d6137
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

gerrit-server/src/main/java/com/google/gerrit/server/query/AndPredicate.java

@@ -94,6 +94,8 @@ public class AndPredicate<T> extends Predicate<T> {
 
   @Override
   public boolean equals(final Object other) {
+    if (other == null)
+      return false;
     return getClass() == other.getClass()
         && getChildren().equals(((Predicate<?>) other).getChildren());
   }