docs: private MonthCellWithMonthIndex getMonthCellWithIndexByDate(Date date) {
      Calendar searchCal = Calendar.getInstance(timeZone, locale);
      searchCal.setTime(date);
      String monthKey = monthKey(searchCal);
      Calendar actCal = Calendar.getInstance(timeZone, locale);
  
      int index = cells.getIndexOfKey(monthKey);
      List<List<MonthCellDescriptor>> monthCells = cells.get(monthKey);
      for (List<MonthCellDescriptor> weekCells : monthCells) {
        for (MonthCellDescriptor actCell : weekCells) {
          actCal.setTime(actCell.getDate());
          if (sameDate(actCal, searchCal) && actCell.isSelectable()) {
            return new MonthCellWithMonthIndex(actCell, index);
          }
        }
      }
      return null;
    }