@NotNull
  private static Map<TraceElement, List<TraceElement>> toEmptyMap(@NotNull Map<Integer, TraceElement> order) {
    return order.keySet().stream().collect(Collectors.toMap(order::get, x -> Collections.emptyList()));
  }
@NotNull
  private static Map<TraceElement, List<TraceElement>> toEmptyMap(@NotNull Map<Integer, TraceElement> order)