add json->'key'=null support

src/client/src/tscSQLParser.c

@@ -4731,7 +4731,7 @@ static int32_t handleExprInQueryCond(SSqlCmd* pCmd, SQueryInfo* pQueryInfo, tSql
     if (pRight->tokenId == TK_NULL && (*pExpr)->tokenId == TK_EQ) {
       // transform for json->'key'=null
       pRight->tokenId = TK_STRING;
-      pRight->value.nType = TSDB_DATA_TYPE_BINARY;
+      pRight->value.nType = TSDB_DATA_TYPE_NCHAR;
       pRight->value.nLen = INT_BYTES;
       pRight->value.pz = calloc(INT_BYTES, 1);
       *(uint32_t*)pRight->value.pz = TSDB_DATA_JSON_null;