if (gratuityEvent.isOpen()) {
if (gratuityEvent.isInDebt()) {
    public Set<GratuityEvent> getNotPayedGratuityEvents() {	final Set<GratuityEvent> result = new HashSet<GratuityEvent>();		for (final GratuityEvent gratuityEvent : getGratuityEvents()) {	    if (gratuityEvent.isOpen()) {		result.add(gratuityEvent);	    }	}	return result;    }