How to perform the parameter type check in golang gin using validator?

Question

I have a Validator struct like this

type UploadFileFormValidator struct {
    File       []*multipart.FileHeader `form:"File" binding:"required,min=1"`
    InputKey   string                  `form:"Key" binding:"disallowed-char"`
    Permission string                  `form:"Permission" binding:"disallowed-permission"`
}

and using it like below

func Bind(c *gin.Context, obj interface{}) error {
    b := binding.Default(c.Request.Method, c.ContentType())
    return c.ShouldBindWith(obj, b)
}

and format my errors like this

func NewValidatorError(err error) CommonError {
    res := CommonError{}
    res.Errors = make(map[string]interface{})

    errs := err.(validator.ValidationErrors)

    for _, v := range errs {
        if v.Param() != "" {
            res.Errors[v.Field()] = fmt.Sprintf("{%v: %v}", v.Tag(), v.Param())
        } else {
            res.Errors[v.Field()] = fmt.Sprintf("{key: %v}", v.Tag())
        }
    }

    return res
}

But the problem is when I upload a file in InputKey or Permission fields I won't get validator.ValidationErrors as expected.

It's like gin treat this situation as some other kinds of errors.

How can I perform a parameter type check and still using the origin code structure?