@Override //Comparator
    public int compare(Event o1, Event o2) {// Bigger means ends later
        if (o1.getEnd() == null && o2.getEnd() != null) return -1;//o1 bigger --> Havent started yet!
        if (o1.getEnd() != null && o2.getEnd() == null) return 1;//o2 bigger
        if (o1.getEnd() == null && o2.getEnd() == null) return 0;//Neither

        return o1.getEnd().compareTo(o2.getEnd());
    }