Moving Dist flow rule store backup mechanism to use EC Map

Change-Id: I465cc2424004721bf09505ac9cde068884f04940

@@ -22,7 +22,7 @@ import org.onosproject.net.DeviceId;
 import org.slf4j.Logger;
 
 public class DefaultFlowEntry extends DefaultFlowRule
-    implements FlowEntry, StoredFlowEntry {
+    implements StoredFlowEntry {
 
     private static final Logger log = getLogger(DefaultFlowEntry.class);
 

@@ -357,6 +357,10 @@ public class EventuallyConsistentMapImpl<K, V>
     }
 
     private boolean removeInternal(K key, Timestamp timestamp) {
+        if (timestamp == null) {
+            return false;
+        }
+
         counter.incrementCount();
         final MutableBoolean updated = new MutableBoolean(false);