Skip variable add Type-Check if node value is NULL

src/server/ua_services_nodemanagement.c

@@ -190,7 +190,7 @@ typeCheckVariableNode(UA_Server *server, UA_Session *session,
     }
 
     /* Typecheck the value */
-    if(value.hasValue) {
+    if(value.hasValue && value.value.data) {
         /* If the type-check failed write the same value again. The
          * write-service tries to convert to the correct type... */
         if(!compatibleValue(server, session, &node->dataType, node->valueRank,