@Override
    public SortedSet<V> get() {
      return new TreeSet<>(comparator);
    }
  }

  private static final class EnumSetSupplier<V extends Enum<V>>
      implements Supplier<Set<V>>, Serializable {
    private final Class<V> clazz;

    EnumSetSupplier(Class<V> clazz) {
      this.clazz = checkNotNull(clazz);
    }

    @Override
    public Set<V> get() {