Return immediately when the given BatchWrite is empty

This revision aims to remove empty check of BatchWrite in the caller
side of this method

Change-Id: Ic0d659a6da221a052ad135eba18a783caa81ec42

@@ -112,6 +112,7 @@ public interface IntentStore extends Store<IntentEvent, IntentStoreDelegate> {
 
     /**
      * Execute writes in a batch.
+     * If the specified BatchWrite is empty, write will not be executed.
      *
      * @param batch BatchWrite to execute
      * @return failed operations

@@ -54,6 +54,7 @@ import org.onlab.util.KryoNamespace;
 import org.slf4j.Logger;
 
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.EnumSet;
 import java.util.HashSet;
 import java.util.List;
@@ -416,6 +417,9 @@ public class DistributedIntentStore
 
     @Override
     public List<Operation> batchWrite(BatchWrite batch) {
+        if (batch.isEmpty()) {
+            return Collections.emptyList();
+        }
 
         List<Operation> failed = new ArrayList<>();
         final Builder builder = BatchWriteRequest.newBuilder();

@@ -54,6 +54,7 @@ import org.onlab.util.KryoNamespace;
 import org.slf4j.Logger;
 
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.EnumSet;
 import java.util.List;
 import java.util.Map;
@@ -394,6 +395,10 @@ public class HazelcastIntentStore
 
     @Override
     public List<Operation> batchWrite(BatchWrite batch) {
+        if (batch.isEmpty()) {
+            return Collections.emptyList();
+        }
+
         // Hazelcast version will never fail for conditional failure now.
         List<Operation> failed = new ArrayList<>();
 

@@ -33,6 +33,7 @@ import org.onosproject.net.intent.BatchWrite.Operation;
 import org.onosproject.store.AbstractStore;
 import org.slf4j.Logger;
 
+import java.util.Collections;
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
@@ -154,6 +155,10 @@ public class SimpleIntentStore
      */
     @Override
     public List<Operation> batchWrite(BatchWrite batch) {
+        if (batch.isEmpty()) {
+            return Collections.emptyList();
+        }
+
         List<Operation> failed = Lists.newArrayList();
         for (Operation op : batch.operations()) {
             switch (op.type()) {