ONOS-4690: containsKey() in TransactionalMap

Change-Id: I13a5eea3871a9a6cc5f808b662584d1892ff19bd
diff --git a/core/store/primitives/src/main/java/org/onosproject/store/primitives/impl/DefaultTransactionalMap.java b/core/store/primitives/src/main/java/org/onosproject/store/primitives/impl/DefaultTransactionalMap.java
index c96b20a..d138c9b 100644
--- a/core/store/primitives/src/main/java/org/onosproject/store/primitives/impl/DefaultTransactionalMap.java
+++ b/core/store/primitives/src/main/java/org/onosproject/store/primitives/impl/DefaultTransactionalMap.java
@@ -109,6 +109,11 @@
     }
 
     @Override
+    public boolean containsKey(K key) {
+        return get(key) != null;
+    }
+
+    @Override
     public V put(K key, V value) {
         checkState(txContext.isOpen(), TX_CLOSED_ERROR);
         checkNotNull(value, ERROR_NULL_VALUE);