code: func (g *Cloud) encodeDiskTags(tags map[string]string) (string, error) {
  	if len(tags) == 0 {
  		// No tags -> empty JSON
  		return "", nil
  	}
  
  	enc, err := json.Marshal(tags)
  	if err != nil {
  		return "", err
  	}
  	return string(enc), nil
  }
docs: // encodeDiskTags encodes requested volume tags into JSON string, as GCE does
  // not support tags on GCE PDs and we use Description field as fallback.