code: public static List<Track> nonEmptyTracks(final List<Track> tracks) {
  		return tracks.stream()
  			.map(track -> track.toBuilder()
  				.listMap(Filters::nonEmptySegments)
  				.build())
  			.filter(Track::nonEmpty)
  			.collect(toList());
  	}
docs: Return a new track list with all <i>empty</i> tracks removed.
  
  @param tracks the track list to clean up
  @return a new track list with all <i>empty</i> tracks removed
  @throws NullPointerException if the given argument is {@code null}