Remove dereferencing a null pointer

Change-Id: I89fd14f62da41622b18fb117f7ceed9d2c2fc7df
diff --git a/apps/tenbi/utils/src/main/java/org/onosproject/teyang/utils/topology/LinkConverter.java b/apps/tenbi/utils/src/main/java/org/onosproject/teyang/utils/topology/LinkConverter.java
index b1c36db52..8869110 100644
--- a/apps/tenbi/utils/src/main/java/org/onosproject/teyang/utils/topology/LinkConverter.java
+++ b/apps/tenbi/utils/src/main/java/org/onosproject/teyang/utils/topology/LinkConverter.java
@@ -1009,6 +1009,7 @@
     public static TeLinkEvent teNetworkLink2yangTeLinkEvent(TeTopologyEventTypeEnum eventType,
                                                             NetworkLinkEventSubject linkData,
                                                             TeTopologyService teTopologyService) {
+        checkNotNull(linkData);
         TeLinkEvent.TeLinkEventBuilder teLinkEventBuilder = new DefaultTeLinkEvent.TeLinkEventBuilder();
 
         TeTopologyEventType yangEventType = new TeTopologyEventType(eventType);