code: func AdditionalItemsNotAllowed(name, in string) *Validation {
  	msg := fmt.Sprintf(noAdditionalItems, name, in)
  	if in == "" {
  		msg = fmt.Sprintf(noAdditionalItemsNoIn, name)
  	}
  	return &Validation{
  		code:    NoAdditionalItemsCode,
  		Name:    name,
  		In:      in,
  		message: msg,
  	}
  }
docs: // AdditionalItemsNotAllowed an error for invalid additional items