Refactor: fix the issues reported by static code analyzer

Change-Id: I8421b5d750e14012d30176ddca7a3873539a361b
diff --git a/apps/openstacknode/api/src/main/java/org/onosproject/openstacknode/api/OpenstackNodeEvent.java b/apps/openstacknode/api/src/main/java/org/onosproject/openstacknode/api/OpenstackNodeEvent.java
index 5962245..ae64e28 100644
--- a/apps/openstacknode/api/src/main/java/org/onosproject/openstacknode/api/OpenstackNodeEvent.java
+++ b/apps/openstacknode/api/src/main/java/org/onosproject/openstacknode/api/OpenstackNodeEvent.java
@@ -22,6 +22,9 @@
  */
 public class OpenstackNodeEvent extends AbstractEvent<OpenstackNodeEvent.Type, OpenstackNode> {
 
+    /**
+     * List of openstack node event types.
+     */
     public enum Type {
 
         /**