code: func (r *multipartRequest) TrySet(value reflect.Value, field reflect.StructField, key string, opt setOptions) (isSetted bool, err error) {
  	if value.Type() == multipartFileHeaderStructType {
  		_, file, err := (*http.Request)(r).FormFile(key)
  		if err != nil {
  			return false, err
  		}
  		if file != nil {
  			value.Set(reflect.ValueOf(*file))
  			return true, nil
  		}
  	}
  
  	return setByForm(value, field, r.MultipartForm.Value, key, opt)
  }
docs: // TrySet tries to set a value by the multipart request with the binding a form file