class ListingConnector implements IndexingConnector, ItemRetriever,
    IncrementalChangeHandler {

  @Override
  public void traverse() throws IOException, InterruptedException {
    if (!doTraverse("full traversal", CHECKPOINT_FULL, repository::getIds)) {
      throw new NullPointerException("getIds returned null");
    }
  }

  public  ListingConnector(Repository repository);
  public  ListingConnector(Repository repository, CheckpointHandler checkpointHandler);

}