Fix to return empty list not null if there is no rows in Controller table

Change-Id: If1ff8c229cfafdd25c5cef4029c6f31dc5cfb6d8
diff --git a/ovsdb/api/src/main/java/org/onosproject/ovsdb/controller/driver/DefaultOvsdbClient.java b/ovsdb/api/src/main/java/org/onosproject/ovsdb/controller/driver/DefaultOvsdbClient.java
index 2575a25..3280ad3 100644
--- a/ovsdb/api/src/main/java/org/onosproject/ovsdb/controller/driver/DefaultOvsdbClient.java
+++ b/ovsdb/api/src/main/java/org/onosproject/ovsdb/controller/driver/DefaultOvsdbClient.java
@@ -175,14 +175,19 @@
      *
      * @param dbName    the ovsdb database name
      * @param tableName the ovsdb table name
-     * @return ovsRowStore, empty if row store is find
+     * @return ovsRowStore, empty store if no rows exist in the table
      */
     private OvsdbRowStore getRowStore(String dbName, String tableName) {
         OvsdbTableStore tableStore = getTableStore(dbName);
         if (tableStore == null) {
             return null;
         }
-        return tableStore.getRows(tableName);
+
+        OvsdbRowStore rowStore = tableStore.getRows(tableName);
+        if (rowStore == null) {
+            rowStore = new OvsdbRowStore();
+        }
+        return rowStore;
     }
 
     /**