@CheckReturnValue
    @NonNull
    @BackpressureSupport(BackpressureKind.FULL)
    @SchedulerSupport(SchedulerSupport.NONE)
    public final <U, R> Flowable<R> flatMap(final Function<? super T, ? extends Publisher<? extends U>> mapper,
            final BiFunction<? super T, ? super U, ? extends R> combiner, boolean delayErrors, int maxConcurrency, int bufferSize) {
        ObjectHelper.requireNonNull(mapper, "mapper is null");
        ObjectHelper.requireNonNull(combiner, "combiner is null");
        ObjectHelper.verifyPositive(maxConcurrency, "maxConcurrency");
        ObjectHelper.verifyPositive(bufferSize, "bufferSize");
        return flatMap(FlowableInternalHelper.flatMapWithCombiner(mapper, combiner), delayErrors, maxConcurrency, bufferSize);
    }