@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Completable switchMapCompletableDelayError(@NonNull Function<? super T, ? extends CompletableSource> mapper) {
        ObjectHelper.requireNonNull(mapper, "mapper is null");
        return RxJavaPlugins.onAssembly(new ObservableSwitchMapCompletable<T>(this, mapper, true));
    }