Unit tests for the distributed group store.

Change-Id: Ie8f00b9bbc1ba46a6f80e70f63d1fd853d64154b
diff --git a/core/api/src/test/java/org/onosproject/store/service/TestEventuallyConsistentMap.java b/core/api/src/test/java/org/onosproject/store/service/TestEventuallyConsistentMap.java
index 5ee44c4..4f612de 100644
--- a/core/api/src/test/java/org/onosproject/store/service/TestEventuallyConsistentMap.java
+++ b/core/api/src/test/java/org/onosproject/store/service/TestEventuallyConsistentMap.java
@@ -91,7 +91,9 @@
         EventuallyConsistentMapEvent<K, V> addEvent =
                 new EventuallyConsistentMapEvent<>(mapName, PUT, key, value);
         notifyListeners(addEvent);
-        peerUpdateFunction.apply(key, value);
+        if (peerUpdateFunction != null) {
+            peerUpdateFunction.apply(key, value);
+        }
     }
 
     @Override