Merge pull request #15772 from jasontedor/test-cluster-service-no-timeout

Fix NPE in TestClusterService when waiting indefinitely

test/framework/src/main/java/org/elasticsearch/test/cluster/TestClusterService.java

@@ -184,9 +184,11 @@ public class TestClusterService implements ClusterService {
         if (threadPool == null) {
             throw new UnsupportedOperationException("TestClusterService wasn't initialized with a thread pool");
         }
+        if (timeout != null) {
             NotifyTimeout notifyTimeout = new NotifyTimeout(listener, timeout);
             notifyTimeout.future = threadPool.schedule(timeout, ThreadPool.Names.GENERIC, notifyTimeout);
             onGoingTimeouts.add(notifyTimeout);
+        }
         listeners.add(listener);
         listener.postAdded();
     }