Fix: Add missing decode method for MappingInstructionCodec

Change-Id: I94af9585a4b622e6320e2e43f40004947b686fa2
diff --git a/apps/mappingmanagement/web/src/main/java/org/onosproject/mapping/web/codec/MappingInstructionCodec.java b/apps/mappingmanagement/web/src/main/java/org/onosproject/mapping/web/codec/MappingInstructionCodec.java
index dff9133..96b4a7c 100644
--- a/apps/mappingmanagement/web/src/main/java/org/onosproject/mapping/web/codec/MappingInstructionCodec.java
+++ b/apps/mappingmanagement/web/src/main/java/org/onosproject/mapping/web/codec/MappingInstructionCodec.java
@@ -49,4 +49,13 @@
 
         return new EncodeMappingInstructionCodecHelper(instruction, context).encode();
     }
+
+    @Override
+    public MappingInstruction decode(ObjectNode json, CodecContext context) {
+        if (json == null || !json.isObject()) {
+            return null;
+        }
+
+        return new DecodeMappingInstructionCodecHelper(json, context).decode();
+    }
 }