super.releaseResources(reason);
    this.values = null;
  }

  abstract C combine(List<@Nullable Present<V>> values);

  /** Used for {@link Futures#allAsList} and {@link Futures#successfulAsList}. */
  static final class ListFuture<V extends @Nullable Object>
      extends CollectionFuture<V, List<@Nullable V>> {
    ListFuture(
        ImmutableCollection<? extends ListenableFuture<? extends V>> futures,

   * input futures, if all succeed.
   *
   * <p>The list of results is in the same order as the input list.
   *
   * <p>This differs from {@link #successfulAsList(ListenableFuture[])} in that it will return a
   * failed future if any of the items fails.
   *
   * <p>Canceling this future will attempt to cancel all the component futures, and if any of the

   * input futures, if all succeed.
   *
   * <p>The list of results is in the same order as the input list.
   *
   * <p>This differs from {@link #successfulAsList(ListenableFuture[])} in that it will return a
   * failed future if any of the items fails.
   *
   * <p>Canceling this future will attempt to cancel all the component futures, and if any of the