docs: public Interval withPeriodBeforeEnd(ReadablePeriod period) {
          if (period == null) {
              return withDurationBeforeEnd(null);
          }
          Chronology chrono = getChronology();
          long endMillis = getEndMillis();
          long startMillis = chrono.add(period, endMillis, -1);
          return new Interval(startMillis, endMillis, chrono);
      }