I was using python requests to upload file to undertow,
however, if the filename is not encoded in ascii, python will add an encoding info to filename.
captured request snippet:
```
--955c7cd7f78e4a8a9f0df45c35f54d2d
Content-Disposition: form-data; name="file"; filename*=utf-8''%E4%B8%AD%E6%96%87.mp3

ID3.......TCON.......(12)...@]..........@sC..`.H
```

when read this multipart file, undertow will throw an IllegalStateException, say:
UT000018: Form value is a String, use getValue() instead