[ONOS-6874] Implement nullable ConsistentMap

Change-Id: I82a232d376b230b06977b24f12364aa374c9c113
diff --git a/core/store/primitives/src/test/java/org/onosproject/store/primitives/resources/impl/AtomixConsistentMapTest.java b/core/store/primitives/src/test/java/org/onosproject/store/primitives/resources/impl/AtomixConsistentMapTest.java
index 42c6dbc..d08495a 100644
--- a/core/store/primitives/src/test/java/org/onosproject/store/primitives/resources/impl/AtomixConsistentMapTest.java
+++ b/core/store/primitives/src/test/java/org/onosproject/store/primitives/resources/impl/AtomixConsistentMapTest.java
@@ -79,6 +79,44 @@
     }
 
     /**
+     * Tests null values.
+     */
+    @Test
+    public void testNullValues() throws Throwable {
+        final byte[] rawFooValue = Tools.getBytesUtf8("Hello foo!");
+        final byte[] rawBarValue = Tools.getBytesUtf8("Hello bar!");
+
+        AtomixConsistentMap map = newPrimitive("testNullValues");
+
+        map.get("foo")
+                .thenAccept(v -> assertNull(v)).join();
+        map.put("foo", null)
+                .thenAccept(v -> assertNull(v)).join();
+        map.put("foo", rawFooValue).thenAccept(v -> {
+            assertNotNull(v);
+            assertNull(v.value());
+        }).join();
+        map.get("foo").thenAccept(v -> {
+            assertNotNull(v);
+            assertTrue(Arrays.equals(v.value(), rawFooValue));
+        }).join();
+        map.replace("foo", rawFooValue, null)
+                .thenAccept(replaced -> assertTrue(replaced)).join();
+        map.get("foo").thenAccept(v -> {
+            assertNotNull(v);
+            assertNull(v.value());
+        }).join();
+        map.replace("foo", rawFooValue, rawBarValue)
+                .thenAccept(replaced -> assertFalse(replaced)).join();
+        map.replace("foo", null, rawBarValue)
+                .thenAccept(replaced -> assertTrue(replaced)).join();
+        map.get("foo").thenAccept(v -> {
+            assertNotNull(v);
+            assertTrue(Arrays.equals(v.value(), rawBarValue));
+        }).join();
+    }
+
+    /**
      * Tests map event notifications.
      */
     @Test
@@ -274,7 +312,6 @@
         }).join();
     }
 
-
     protected void mapListenerTests() throws Throwable {
         final byte[] value1 = Tools.getBytesUtf8("value1");
         final byte[] value2 = Tools.getBytesUtf8("value2");