HazelcastLinkResourceStore: bug fix for ONOS-379

Change-Id: I783b51d4d937918c0bca9feb09d29263266145ee

@@ -497,7 +497,7 @@ public class HazelcastLinkResourceStore
                 return res;
             }
         }
-        return null;
+        return res;
     }
 
     @Override