Fix javadoc warnings

Change-Id: I3de24a04593f47c786f698f5ee1669b3d2f2fdfc
diff --git a/core/api/src/main/java/org/onosproject/store/service/DistributedPrimitive.java b/core/api/src/main/java/org/onosproject/store/service/DistributedPrimitive.java
index 342a110..6a6c09e 100644
--- a/core/api/src/main/java/org/onosproject/store/service/DistributedPrimitive.java
+++ b/core/api/src/main/java/org/onosproject/store/service/DistributedPrimitive.java
@@ -71,6 +71,7 @@
 
     /**
      * Returns the application owning this primitive.
+     * @return application id
      */
     default ApplicationId applicationId() {
         return null;