}
    return null;
  }

  /**
   * An {@link AbstractTransformFuture} that delegates to an {@link AsyncFunction} and {@link
   * #setFuture(ListenableFuture)}.
   */
  private static final class AsyncTransformFuture<
          I extends @Nullable Object, O extends @Nullable Object>
      extends AbstractTransformFuture<
          I, O, AsyncFunction<? super I, ? extends O>, ListenableFuture<? extends O>> {

    }
    return null;
  }

  /**
   * An {@link AbstractTransformFuture} that delegates to an {@link AsyncFunction} and {@link
   * #setFuture(ListenableFuture)}.
   */
  private static final class AsyncTransformFuture<
          I extends @Nullable Object, O extends @Nullable Object>
      extends AbstractTransformFuture<
          I, O, AsyncFunction<? super I, ? extends O>, ListenableFuture<? extends O>> {

      ListenableFuture<O> transformAsync(
          ListenableFuture<I> input,
          AsyncFunction<? super I, ? extends O> function,
          Executor executor) {
    return AbstractTransformFuture.createAsync(input, function, executor);
  }

  /**
   * Returns a new {@code Future} whose result is derived from the result of the given {@code