* If your task does anything heavier consider, just using a listener with an executor.
   *
   * @since 20.0
   */
  @ForOverride
  protected void afterDone() {}

  // TODO(b/114236866): Inherit doc from InternalFutureFailureAccess. Also, -link to its URL.
  /**
   * Usually returns {@code null} but, if this {@code Future} has failed, may <i>optionally</i>