@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.CUSTOM)
    public final Observable<T> delay(long delay, TimeUnit unit, Scheduler scheduler, boolean delayError) {
        ObjectHelper.requireNonNull(unit, "unit is null");
        ObjectHelper.requireNonNull(scheduler, "scheduler is null");

        return RxJavaPlugins.onAssembly(new ObservableDelay<T>(this, delay, unit, scheduler, delayError));
    }