@NotNull
  public LibraryRootsDetector getRootsDetector() {
    final List<? extends RootDetector> detectors = getRootDetectors();
    if (detectors.isEmpty()) {
      throw new IllegalStateException("Detectors list is empty for " + this);
    }
    return new LibraryRootsDetectorImpl(detectors);
  }
@NotNull
  public LibraryRootsDetector getRootsDetector()