code: func dateOrZero(datestr, format string) (time.Time, error) {
  	if datestr == "" {
  		return time.Time{}, nil
  	}
  	if format == "" {
  		format = time.RFC3339
  	}
  	return time.Parse(format, datestr)
  }
docs: // dateOrZero parses datestr with the given format and returns the resulting
  // time and error. An empty datestr is not an error and yields a zero time. format
  // defaults to time.RFC3339 if empty.