@Override
	public int compare(Drillable one, Drillable two) {
		Date date1 = one.getPractice() == null ? null : one.getPractice().getLastPracticed();
		Date date2 = two.getPractice() == null ? null : two.getPractice().getLastPracticed();
		
		if (date1 == null && date2 == null) {
			return 0;
		}
		if (date1 == null) {
			return -1;
		}
		if (date2 == null) {
			return 1;
		}
		return date1.compareTo(date2);
	}