public CashOffice registerCashOffice(CashOffice cashOffice) {
    int index = cashOffices.indexOf(cashOffice);
    if (index == -1) {
      addCashOffice(cashOffice);
      return cashOffice;
    } else {
      CashOffice foundedCashOffice = cashOffices.get(index);
      //      Iterator<Ticket> tickets = cashOffice.tiketsIterator();
      //      while (tickets.hasNext()) {
      //        foundedCashOffice.addTicket(tickets.next());
      //      }
      return foundedCashOffice;
    }
  }