2.1.7 stream load 报错： can not cast from origin type bitmap to target type=varchar(65533)

版本：
doris-2.1.7-rc03

问题描述：
建表语句中包含bitmap类型，导入时使用to_bitmap提供值，但会报语法错误

建表：

create table test_load_bitmap
(tiny_1  TINYINT,
 small_1 SMALLINT,
 bit_1 bitmap BITMAP_UNION
);

加载：

curl --location-trusted -u root:123456abc_  \
-H"columns:bit_1= to_bitmap(small_1)" \
-T ./file   \
http://fe_ip:fe_http_port/api/db/test_load_bitmap/_stream_load

报错：

{
    "TxnId": 50630,
    "Label": "4a3c7994-4d20-478a-bd66-96d255c24f3c",
    "Comment": "",
    "TwoPhaseCommit": "false",
    "Status": "Fail",
    "Message": "[ANALYSIS_ERROR]TStatus: errCode = 2, detailMessage = can not cast from origin type bitmap to target type=varchar(65533)",
    "NumberTotalRows": 0,
    "NumberLoadedRows": 0,
    "NumberFilteredRows": 0,
    "NumberUnselectedRows": 0,
    "LoadBytes": 0,
    "LoadTimeMs": 0,
    "BeginTxnTimeMs": 1,
    "StreamLoadPutTimeMs": 8,
    "ReadDataTimeMs": 0,
    "WriteDataTimeMs": 0,
    "ReceiveDataTimeMs": 0,
    "CommitAndPublishTimeMs": 0
}

我的问题：
我的用法应该符合stream load和bitmap的使用规范，这个报错应该不合理，能否修复？
是否有其它手段可以规避该问题？