@Contract("!null -> !null; null -> null")
  public static Set<File> unmodifiableFileSet(@Nullable Collection<String> paths) {
    if (paths == null) return null;
    if (paths.isEmpty()) return Collections.emptySet();
    LinkedHashSet<File> files = new LinkedHashSet<>(paths.size());
    for (String path : paths) {
      if (path != null) {
        files.add(new File(path));
      }
    }
    return Collections.unmodifiableSet(files);
  }
@Contract("!null -> !null; null -> null")
  public static Set<File> unmodifiableFileSet(@Nullable Collection<String> paths)