asp.net core 上传图片接口返回The input was not valid

   [Route("api/[controller]/[action]"),ApiExplorerSettings(GroupName = "hello")]
   [ApiController]
    public class UploadFileController : ControllerBase
    {
        public UploadFileController()
        {
            
        }

        [HttpPost]
        public string UploadSingle(UploadReqModel ufile)
        {
            try
            {
                var file = ufile.file;
                string key = string.IsNullOrEmpty(ufile.key) ? "def" : ufile.key;
                return new  QiNiuUpload.UploadFilesHelper().UploadFile(file, ufile.key, ufile.isPrivate);
            }
            catch (Exception ex)
            {
                new LogHelper().Error(ex, string.Format("{0}.{1}:", RouteData.Values["controller"].ToString(), RouteData.Values["action"].ToString()) + ex.Message);
                return JsonHelper.Instance.Serialize(new { errcode = 500, errmsg = "上传失败！" });
            }
        }