public function mergeHolidayLists(array $holidayLists)
    {
        $newList = new HolidayList();
        foreach ($holidayLists as $holidayList) {
            foreach ($holidayList->getList() as $holiday) {
                $newList->add($holiday);
            }
        }

        return (new SortByDateFilter())->filter($newList);
    }