code: func (v *Volumes) HashString() string {
  	if v == nil {
  		return ""
  	}
  	result := []string{}
  	for _, vol := range v.Volumes {
  		result = append(result, vol.String())
  	}
  	sort.Strings(result)
  	return strings.Join(result, ",")
  }
docs: // Generate a hash string to detect service volume config changes