[ONOS-2499]update accordingly for ONOS-2408's review recommendation

Change-Id: I24e7c4acbe38e4286b994c5bf50d22def945fb29
diff --git a/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/message/RowUpdate.java b/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/message/RowUpdate.java
index db11edd..221206e 100644
--- a/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/message/RowUpdate.java
+++ b/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/message/RowUpdate.java
@@ -40,7 +40,7 @@
      * @param newRow present for "initial", "insert", and "modify" updates
      */
     public RowUpdate(UUID uuid, Row oldRow, Row newRow) {
-        checkNotNull(uuid, "uuid is not null");
+        checkNotNull(uuid, "uuid cannot be null");
         this.uuid = uuid;
         this.oldRow = oldRow;
         this.newRow = newRow;