@CheckReturnValue
    @NonNull
    public final <R> ParallelFlowable<R> concatMapDelayError(
            @NonNull Function<? super T, ? extends Publisher<? extends R>> mapper,
                    int prefetch, boolean tillTheEnd) {
        ObjectHelper.requireNonNull(mapper, "mapper is null");
        ObjectHelper.verifyPositive(prefetch, "prefetch");
        return RxJavaPlugins.onAssembly(new ParallelConcatMap<T, R>(
                this, mapper, prefetch, tillTheEnd ? ErrorMode.END : ErrorMode.BOUNDARY));
    }