* to {@code statusFuture} <i>in addition to</i> the call you make to {@link #finishToFuture()} or
   * a derivation method <i>on the same instance</i>. This is important because calling {@code
   * statusFuture} alone does not provide a way to close the pipeline.
   */
  public ListenableFuture<?> statusFuture() {
    return nonCancellationPropagating(future.transform(constant(null), directExecutor()));
  }

  /**