BGP connection collision detection.

Change-Id: I124674b79170450409df5d0f4b5fea5f9e11f1d9

@@ -151,7 +151,9 @@ class BGPNotificationMsgVer4 implements BGPNotificationMsg {
 
         @Override
         public Builder setData(byte[] data) {
+            if (data != null) {
                 this.data = data;
+            }
             return this;
         }