code: func getStartEndTimeHistorical(request *restful.Request) (time.Time, time.Time, error) {
  	start, end, err := getStartEndTime(request)
  	if err != nil {
  		return start, end, err
  	}
  
  	if start.IsZero() {
  		return start, end, fmt.Errorf("no start time (or a start time of zero) provided")
  	}
  
  	return start, end, err
  }
docs: // getStartEndTimeHistorical fetches the start and end times of the request.  Unlike
  // getStartEndTime, this function returns an error if the start time is not passed
  // (or is zero, since many things in go use time.Time{} as an empty value) --
  // different sinks have different defaults, and certain sinks have issues if an actual
  // time of zero (i.e. the epoch) is used (because that would be too many data points
  // to consider in certain cases).  Require applications to pass an explicit start time
  // that they can deal with.