Return empty discovery stats

Author: jasontedor

core/src/main/java/org/elasticsearch/discovery/single/SingleNodeDiscovery.java

@@ -34,6 +34,8 @@
 import org.elasticsearch.discovery.Discovery;
 import org.elasticsearch.discovery.DiscoverySettings;
 import org.elasticsearch.discovery.DiscoveryStats;
+import org.elasticsearch.discovery.zen.PendingClusterStateStats;
+import org.elasticsearch.discovery.zen.PendingClusterStatesQueue;
 
 import java.io.IOException;
 import java.util.Collections;
@@ -78,7 +80,7 @@ public void publish(final ClusterChangedEvent event, final AckListener listener)
 
     @Override
     public DiscoveryStats stats() {
-        return null;
+        return new DiscoveryStats((PendingClusterStateStats) null);
     }
 
     @Override