class UniOnItemTransformToMulti extends AbstractMulti<O> {

    @Override
    public void subscribe(MultiSubscriber<? super O> subscriber) {
        if (subscriber == null) {
            throw new NullPointerException("The subscriber must not be `null`");
        }
        AbstractUni.subscribe(upstream, new FlatMapPublisherSubscriber<>(subscriber, mapper));
    }

    public  UniOnItemTransformToMulti(Uni<I> upstream, Function<? super I, ? extends Publisher<? extends O>> mapper);

}