code: func Required(name, in string) *Validation {
  	var msg string
  	if in == "" {
  		msg = fmt.Sprintf(requiredFailNoIn, name)
  	} else {
  		msg = fmt.Sprintf(requiredFail, name, in)
  	}
  	return &Validation{
  		code:    RequiredFailCode,
  		Name:    name,
  		In:      in,
  		message: msg,
  	}
  }
docs: // Required error for when a value is missing