/**
  * @param DayAttendance $dayAttendance
  */
 private function addDayAttendance(DayAttendance $dayAttendance)
 {
     $date = $dayAttendance->getArrival()->format('Y-m-d');
     if (isset($this->dayAttendanceList[$date])) {
         throw new \InvalidArgumentException();
     }
     $this->dayAttendanceList[$date] = $dayAttendance;
 }