code: public static List<Route> nonEmptyRoutes(final List<Route> routes) {
  		return routes.stream()
  			.filter(Route::nonEmpty)
  			.collect(toList());
  	}
docs: Return a new route list with all <i>empty</i> routes removed.
  
  @param routes the route list to clean up
  @return a new route list with all <i>empty</i> routes removed
  @throws NullPointerException if the given argument is {@code null}