Grouping map entries with Java 8 v2

gistfile1.java

public static Map<LocalDate, Integer> summarizePeriods(final List<Bike> bikes, final Predicate<Map.Entry<LocalDate, Integer>> entryFilter) {	
  return bikes.stream()
    .filter(Bike::hasMilages)
    .flatMap(bike -> bike.getPeriods().entrySet().stream())			
    .filter(Optional.ofNullable(entryFilter).orElse(entry -> true))
    .collect(
      Collectors.groupingBy(
        Map.Entry::getKey,
        Collectors.reducing(0, Map.Entry::getValue, Integer::sum)
      )
    );
}