List<IEmployee> employees = new ArrayList<IEmployee>();
Set<IEmployee> employees = new HashSet<IEmployee>();
    public List<IEmployee> getWorkingEmployees(Date begin, Date end) {        IUnit unit = this.getUnit();        List<IEmployee> employees = new ArrayList<IEmployee>();        if (unit != null) {            for (IContract contract : unit.getWorkingContracts(begin, end)) {                                employees.add(contract.getEmployee());                            }            for (IUnit subUnit : unit.getSubUnits()) {                for (IContract contract : subUnit.getWorkingContracts(begin, end)) {                                                         employees.add(contract.getEmployee());                                    }            }        }        return employees;    }