[ONOS-5916] Add a mapping instruction interface with impl classes

Change-Id: I21399cd9853fe4604641af5ad57cd61f02cf354c
diff --git a/apps/mappingmanagement/api/src/main/java/org/onosproject/mapping/DefaultMappingValue.java b/apps/mappingmanagement/api/src/main/java/org/onosproject/mapping/DefaultMappingValue.java
index 3987218..2575764 100644
--- a/apps/mappingmanagement/api/src/main/java/org/onosproject/mapping/DefaultMappingValue.java
+++ b/apps/mappingmanagement/api/src/main/java/org/onosproject/mapping/DefaultMappingValue.java
@@ -15,8 +15,23 @@
  */
 package org.onosproject.mapping;
 
+import org.onosproject.mapping.address.MappingAddress;
+import org.onosproject.mapping.instructions.MappingInstruction;
+
+import java.util.List;
+
 /**
  * Default mapping value implementation.
  */
 public class DefaultMappingValue implements MappingValue {
+
+    @Override
+    public MappingAddress address() {
+        return null;
+    }
+
+    @Override
+    public List<MappingInstruction> instructions() {
+        return null;
+    }
 }