How to validate string is either nil or longer than 0

[evgeniy-ivlev-archie]

Hello.

I need the string to either be nil or longer than 0.

func init() {
	validate = validator.New()

	validate.RegisterValidation("nil_or_non_empty_string", func(fl validator.FieldLevel) bool {
                // NOTHING WORKS HERE
                // I CANNOT DETECT NIL POINTER
         
		v := fl.Field()

		if v.IsNil() {
			return true
		}

		if v.String() != "" {
			return true
		}

		return false
        }
}

Can someone please help me?
Thanks kindly