code: public SortedSet<TimeInterval> getTimeGapIntervals() {
  		SortedSet<TimeInterval> flattenedIntervals = getFlattenedIntervals();
  		SortedSet<TimeInterval> gaps = new TreeSet<TimeInterval>();
  
  		TimeInterval previous = null;
  		for (TimeInterval timeInterval : flattenedIntervals) {
  			if (previous != null) {
  				long from = previous.getTo();
  				long to = timeInterval.getFrom();
  				TimeInterval gap = new TimeInterval(from, to);
  				gaps.add(gap);
  			}
  			previous = timeInterval;
  		}
  
  		return gaps;
  	}
docs: Gets a set of intervals representing the times that are NOT represented
  in this timeline.
  
  @return