ONOS-1950 - NPE if intent state is null

Change-Id: I5e93cf57f3c881e5528e3ac522f95451fab70fba
diff --git a/core/common/src/main/java/org/onosproject/codec/impl/IntentCodec.java b/core/common/src/main/java/org/onosproject/codec/impl/IntentCodec.java
index 6b50718..a45ae87 100644
--- a/core/common/src/main/java/org/onosproject/codec/impl/IntentCodec.java
+++ b/core/common/src/main/java/org/onosproject/codec/impl/IntentCodec.java
@@ -49,7 +49,9 @@
 
         IntentService service = context.getService(IntentService.class);
         IntentState state = service.getIntentState(intent.key());
-        result.put("state", state.toString());
+        if (state != null) {
+            result.put("state", state.toString());
+        }
 
         return result;
     }