public <V extends @Nullable Object> ClosingFuture<V> call(
        CombiningCallable<V> combiningCallable, Executor executor) {
      Callable<V> callable =
          new Callable<V>() {
            @Override
            @ParametricNullness
            public V call() throws Exception {
              return new Peeker(inputs).call(combiningCallable, closeables);
            }

            @Override

    public <V extends @Nullable Object> ClosingFuture<V> call(
        CombiningCallable<V> combiningCallable, Executor executor) {
      Callable<V> callable =
          new Callable<V>() {
            @Override
            @ParametricNullness
            public V call() throws Exception {
              return new Peeker(inputs).call(combiningCallable, closeables);
            }

            @Override

      return waitFor(asyncClosingFunction, AsyncClosingFunction.class);
    }

    @SuppressWarnings("unchecked") // proxy for a generic class
    <V> CombiningCallable<V> waitFor(CombiningCallable<V> combiningCallable) {
      return waitFor(combiningCallable, CombiningCallable.class);
    }

    @SuppressWarnings("unchecked") // proxy for a generic class