diff --git a/src/client/src/tscServer.c b/src/client/src/tscServer.c
index 66ca4faa616236d2189314e10def4a3abbf50808..59bcdd691d6a8cfe2f2e65da0c87da9c232fee57 100644
--- a/src/client/src/tscServer.c
+++ b/src/client/src/tscServer.c
@@ -181,9 +181,16 @@ void tscProcessHeartBeatRsp(void *param, TAOS_RES *tres, int code) {
 void tscProcessActivityTimer(void *handle, void *tmrId) {
   int64_t rid = (int64_t) handle;
   STscObj *pObj = taosAcquireRef(tscRefId, rid);
-  if (pObj == NULL) return; 
+  if (pObj == NULL) {
+    return;
+  }
 
   SSqlObj* pHB = taosAcquireRef(tscObjRef, pObj->hbrid);
+  if (pHB == NULL) {
+    taosReleaseRef(tscRefId, rid);
+    return;
+  }
+
   assert(pHB->self == pObj->hbrid);
 
   pHB->retry = 0;
diff --git a/tests/script/general/parser/groupby.sim b/tests/script/general/parser/groupby.sim
index fbe4345a21168fe6e22c947451d8ee80304311f9..44bae6f242f12e5a6430df64520631d0ac3af073 100644
--- a/tests/script/general/parser/groupby.sim
+++ b/tests/script/general/parser/groupby.sim
@@ -606,7 +606,7 @@ sql insert into t1 values ('2020-03-27 04:21:16.000', 1)('2020-03-27 04:31:17.00
 sql insert into t2 values ('2020-03-27 04:11:16.000', 1)('2020-03-27 04:11:17.000', 2) ('2020-03-27 04:11:18.000', 3) ('2020-03-27 04:11:19.000', 4) ; 
 sql insert into t2 values ('2020-03-27 04:21:16.000', 1)('2020-03-27 04:31:17.000', 2) ('2020-03-27 04:51:18.000', 3) ('2020-03-27 05:10:19.000', 4) ; 
 
-print =================>td-2236
+print =================>TD-2236
 sql select first(ts),last(ts) from t1 group by c;
 if $rows != 4 then
   return -1