this.future = task;
  }

  /**
   * Returns a future that finishes when this step does. Calling {@code get()} on the returned
   * future returns {@code null} if the step is successful or throws the same exception that would
   * be thrown by calling {@code finishToFuture().get()} if this were the last step. Calling {@code
   * cancel()} on the returned future has no effect on the {@code ClosingFuture} pipeline.
   *

   * {@code k.equals(k2)} implies that {@code k2} is also of type {@code K}. Using a key type for
   * which this may not hold, such as {@code ArrayList}, may risk a {@code ClassCastException} when
   * calling methods on the resulting map view.
   *
   * @since 14.0
   */
  public static <K extends @Nullable Object, V extends @Nullable Object> Map<K, V> asMap(
      Set<K> set, Function<? super K, V> function) {