code: func NewDatalessJsonResult(size uint32, exps ...time.Time) *JsonResult {
  	exp := time.Time{}
  	switch l := len(exps); {
  	case l == 1:
  		exp = exps[0]
  	case l > 1:
  		panic("too many exps")
  	}
  	return &JsonResult{Size: size, Expiration: google_pb.NewTimestamp(exp)}
  }
docs: // NewDatalessJsonResult creates a new JsonResult object without data and with
  // optional expiration time.