docs: public static DateTime getUniversalTimestamp(final GroupByQuery query)
    {
      final Granularity gran = query.getGranularity();
      final String timestampStringFromContext = query.getContextValue(CTX_KEY_FUDGE_TIMESTAMP, "");
  
      if (!timestampStringFromContext.isEmpty()) {
        return DateTimes.utc(Long.parseLong(timestampStringFromContext));
      } else if (Granularities.ALL.equals(gran)) {
        final DateTime timeStart = query.getIntervals().get(0).getStart();
        return gran.getIterable(new Interval(timeStart, timeStart.plus(1))).iterator().next().getStart();
      } else {
        return null;
      }
    }