Serializing batch execution on per-instance basis for intents

Change-Id: Idda3f4a65e78567302d91ba0070e78d435eea8fd
diff --git a/core/net/src/main/java/org/onlab/onos/net/intent/impl/IntentManager.java b/core/net/src/main/java/org/onlab/onos/net/intent/impl/IntentManager.java
index e64fe82..70878c5 100644
--- a/core/net/src/main/java/org/onlab/onos/net/intent/impl/IntentManager.java
+++ b/core/net/src/main/java/org/onlab/onos/net/intent/impl/IntentManager.java
@@ -155,6 +155,9 @@
 
     @Override
     public void execute(IntentOperations operations) {
+        if (operations.operations().isEmpty()) {
+            return;
+        }
         batchService.addIntentOperations(operations);
     }