List<Unit> allInactiveSubUnits = new ArrayList<Unit>();
Set<Unit> allInactiveSubUnits = new HashSet<Unit>();
    public List<Unit> getInactiveSubUnits(Date currentDate) {        List<Unit> allInactiveSubUnits = new ArrayList<Unit>();        for (Unit subUnit : this.getSubUnits()) {            if (!subUnit.isActive(currentDate)) {                allInactiveSubUnits.add(subUnit);            }        }        return allInactiveSubUnits;    }