Avoid NPE when IntentData was not found.

Change-Id: I3cb67c1ad487c8b546056a35ef0412e41d8e4fb1
diff --git a/incubator/net/src/main/java/org/onosproject/incubator/net/virtual/impl/VirtualNetworkIntentService.java b/incubator/net/src/main/java/org/onosproject/incubator/net/virtual/impl/VirtualNetworkIntentService.java
index 191bec2..6c0b34a 100644
--- a/incubator/net/src/main/java/org/onosproject/incubator/net/virtual/impl/VirtualNetworkIntentService.java
+++ b/incubator/net/src/main/java/org/onosproject/incubator/net/virtual/impl/VirtualNetworkIntentService.java
@@ -205,7 +205,9 @@
     @Override
     public IntentState getIntentState(Key intentKey) {
         checkNotNull(intentKey, KEY_NULL);
-        return store.getIntentData(intentKey).state();
+        return Optional.ofNullable(store.getIntentData(intentKey))
+                .map(IntentData::state)
+                .orElse(null);
     }
 
     @Override