fix: bad code merge

source/dnode/mnode/impl/src/mndTopic.c

@@ -502,6 +502,17 @@ static int32_t mndProcessDropTopicReq(SRpcMsg *pReq) {
   }
 
   SMqTopicObj *pTopic = mndAcquireTopic(pMnode, dropReq.name);
+  if (pTopic == NULL) {
+    if (dropReq.igNotExists) {
+      mDebug("topic:%s, not exist, ignore not exist is set", dropReq.name);
+      return 0;
+    } else {
+      terrno = TSDB_CODE_MND_TOPIC_NOT_EXIST;
+      mError("topic:%s, failed to drop since %s", dropReq.name, terrstr());
+      return -1;
+    }
+  }
+
   if (pTopic->refConsumerCnt != 0) {
     mndReleaseTopic(pMnode, pTopic);
     terrno = TSDB_CODE_MND_TOPIC_SUBSCRIBED;