@NotNull
  private static List<VirtualFile> extractVirtualFiles(@NotNull ContentDiffRequest request) {
    List<VirtualFile> files = new ArrayList<>(0);
    for (DiffContent content : request.getContents()) {
      if (content instanceof DocumentContent) continue; // handled by DocumentListener
      if (content instanceof FileContent) {
        files.add(((FileContent)content).getFile());
      }
    }
    return files;
  }
@NotNull
  private static List<VirtualFile> extractVirtualFiles(@NotNull ContentDiffRequest request)