@Override
  public @NotNull DataIndexer<FileType, Void, FileContent> getIndexer() {
    if (USE_MAPPED_INDEX) {
      throw new UnsupportedOperationException();
    }
    return in -> Collections.singletonMap(in.getFileType(), null);
  }
@Override
  public @NotNull DataIndexer<FileType, Void, FileContent> getIndexer()