docs: public DateMidnight withZoneRetainFields(DateTimeZone newZone) {
          newZone = DateTimeUtils.getZone(newZone);
          DateTimeZone originalZone = DateTimeUtils.getZone(getZone());
          if (newZone == originalZone) {
              return this;
          }
          
          long millis = originalZone.getMillisKeepLocal(newZone, getMillis());
          return new DateMidnight(millis, getChronology().withZone(newZone));
      }