@Override
    public void addMeetingNotes(int id, String text) {
        if(text != null) {
            Meeting newMeeting = getMeeting(id);
            if(newMeeting != null) {
                if(newMeeting.getDate().before(timeNow())) {
                    throw new IllegalStateException();
                } else {
                    PastMeetingImpl newPastMeeting = (PastMeetingImpl) newMeeting;
                    newPastMeeting.setNotes(text);
                }
            } else {
                throw new IllegalArgumentException();
            }
        } else {
            throw new NullPointerException();
        }
    }