add json->'key'=null support

src/client/src/tscSQLParser.c

@@ -4733,6 +4733,7 @@ static int32_t handleExprInQueryCond(SSqlCmd* pCmd, SQueryInfo* pQueryInfo, tSql
       pRight->tokenId = TK_STRING;
       pRight->value.nType = TSDB_DATA_TYPE_BINARY;
       pRight->value.nLen = INT_BYTES;
+      pRight->value.pz = calloc(INT_BYTES, 1);
       *(uint32_t*)pRight->value.pz = TSDB_DATA_JSON_null;
     }
   }else{

tests/pytest/stable/json_tag.py

@@ -279,6 +279,8 @@ class TDTestCase:
         tdSql.execute("INSERT INTO db_json_tag_test.jsons1_21 using db_json_tag_test.jsons1 tags('{\"tagint\":11}') values(now, 11, false, \"你就会\")")
         tdSql.execute("INSERT INTO db_json_tag_test.jsons1_22 using db_json_tag_test.jsons1 tags('{\"tagint\":2}') values(now, 2, false, \"你就会\")")
 
+        # test json->'key'=null
+        tdSql.execute("insert into db_json_tag_test.jsons1_9 values('2020-04-17 15:20:00.000', 5, false, 'json19')")
     def stop(self):
         tdSql.close()
         tdLog.success("%s successfully executed" % __file__)