Enable checkstyle rule to find empty code blocks

Enabled checkstyle rule that detects empty code blocks and fixed the
violations that were discovered.

Change-Id: Icc23e028f2bbabc1849ec566923aa125b2486a3b
diff --git a/src/main/java/net/onrc/onos/core/intent/IntentMap.java b/src/main/java/net/onrc/onos/core/intent/IntentMap.java
index e5cae77..2124d25 100644
--- a/src/main/java/net/onrc/onos/core/intent/IntentMap.java
+++ b/src/main/java/net/onrc/onos/core/intent/IntentMap.java
@@ -148,6 +148,7 @@
         Intent intent = getIntent(operation.intent.getId());
         if (intent == null) {
             // TODO error handling
+            return;
         } else {
             setState(intent.getId(), IntentState.DEL_REQ);
         }