code: func (e *ErrVersionNotSupported) Error() string {
  	if e.hostname == "" {
  		return fmt.Sprintf("host does not support %s version %s", e.service, e.version)
  	}
  	return fmt.Sprintf("host %s does not support %s version %s", e.hostname, e.service, e.version)
  }
docs: // Error returns a customized error message.