Fix ClassCastException processing expired messages

patch by Jason Brown; reviewed by tjake for CASSANDRA-7496

CHANGES.txt

@@ -1,4 +1,5 @@
 2.1.0
+ * Fix ClassCastException processing expired messages (CASSANDRA-7496)
  * Fix prepared marker for collections inside UDT (CASSANDRA-7472)
  * Remove left-over populate_io_cache_on_flush and replicate_on_write
    uses (CASSANDRA-7493)

conf/README.txt

@@ -9,3 +9,5 @@ Optional configuration files
 ============================
 
 cassandra-topology.properties: used by PropertyFileSnitch
+
+

src/java/org/apache/cassandra/net/MessagingService.java

@@ -349,19 +349,19 @@ public final class MessagingService implements MessagingServiceMBean
                     });
                 }
 
-                Mutation mutation = (Mutation) ((WriteCallbackInfo) expiredCallbackInfo).sentMessage.payload;
+                if (expiredCallbackInfo.shouldHint())
-
-                try
                 {
-                    if (expiredCallbackInfo.shouldHint())
+                    Mutation mutation = (Mutation) ((WriteCallbackInfo) expiredCallbackInfo).sentMessage.payload;
+
+                    try
                     {
                         return StorageProxy.submitHint(mutation, expiredCallbackInfo.target, null);
                     }
-                }
+                    finally
-                finally
+                    {
-                {
+                        //We serialized a hint so we don't need this mutation anymore
-                    //We serialized a hint so we don't need this mutation anymore
+                        mutation.release();
-                    mutation.release();
+                    }
                 }
 
                 return null;