Added destroy() method to DistributedPrimitive interface
Implement replace method in ConsistentMap
Using Versioned#valueOrNull in place of Versioned#valueOrElse where appropriate

Change-Id: Ief3f3547d589d35f5c821a1c47035f91078e8316
diff --git a/core/api/src/main/java/org/onosproject/store/service/Synchronous.java b/core/api/src/main/java/org/onosproject/store/service/Synchronous.java
index be65382..d938e48 100644
--- a/core/api/src/main/java/org/onosproject/store/service/Synchronous.java
+++ b/core/api/src/main/java/org/onosproject/store/service/Synchronous.java
@@ -15,6 +15,8 @@
  */
 package org.onosproject.store.service;
 
+import java.util.concurrent.CompletableFuture;
+
 /**
  * DistributedPrimitive that is a synchronous (blocking) version of
  * another.
@@ -38,4 +40,9 @@
     public Type type() {
         return primitive.type();
     }
+
+    @Override
+    public CompletableFuture<Void> destroy() {
+        return primitive.destroy();
+    }
 }