code: func generateUserString(username, imageUser string, uid *pb.Int64Value) string {
  	var userstr string
  	if uid != nil {
  		userstr = strconv.FormatInt(uid.GetValue(), 10)
  	}
  	if username != "" {
  		userstr = username
  	}
  	// We use the user from the image config if nothing is provided
  	if userstr == "" {
  		userstr = imageUser
  	}
  	if userstr == "" {
  		return ""
  	}
  	return userstr
  }
docs: // generateUserString generates valid user string based on OCI Image Spec v1.0.0.