add assertion.

src/system/detail/src/vnodeQueryImpl.c

@@ -4951,8 +4951,10 @@ int32_t vnodeSTableQueryPrepare(SQInfo *pQInfo, SQuery *pQuery, void *param) {
  */
 void vnodeDecMeterRefcnt(SQInfo *pQInfo) {
   STableQuerySupportObj *pSupporter = pQInfo->pTableQuerySupporter;
-  assert(pSupporter->numOfMeters >= 1);
-
+  if (pSupporter != NULL) {
+    assert(pSupporter->numOfMeters >= 1);
+  }
+  
   if (pSupporter == NULL || pSupporter->numOfMeters == 1) {
     atomic_fetch_sub_32(&pQInfo->pObj->numOfQueries, 1);
     dTrace("QInfo:%p vid:%d sid:%d meterId:%s, query is over, numOfQueries:%d", pQInfo, pQInfo->pObj->vnode,