Multiplier Component ‚item‘ is not attached to 'Nette\Forms\Form

<?php

namespace App\Forms;

use NasExt\Forms\Controls\DependentSelectBoxData;
use Nette;
use Nette\Application\UI\Form;
use Nette\Localization\ITranslator;
use App\Model;


class CreateRegistrationFormFactory
{
    use Nette\SmartObject;

    /** @var Model\Facades\RegistrationFacade*/
    protected $registrationFacade;
    /** @var Model\Facades\SiteFacade*/
    protected $siteFacade;
    /** @var Model\Facades\OptItemFacade*/
    protected $optItemFacade;

    /** @var ITranslator */
    private $translator;

    /** @var FormFactory */
    private $factory;

    private $locale;


    public function __construct(ITranslator $translator, FormFactory $factory, Model\Facades\RegistrationFacade $registrationFacade,Model\Facades\SiteFacade $siteFacade,Model\Facades\OptItemFacade $optItemFacade)
    {
        $this->translator = $translator;
        $this->factory = $factory;
        $this->registrationFacade = $registrationFacade;
        $this->siteFacade = $siteFacade;
        $this->optItemFacade = $optItemFacade;
    }

    public function translate($word){
        return $this->translator->translate($word);
    }

	/**
	 * @return Form
	 */
	public function create($firstInput,$members,$locale,callable $onSuccess)
	{
		$form = $this->factory->create();
        $this->locale = $locale;

        $form->addSelect('event','Event',$firstInput)->setRequired(TRUE)->setPrompt("Select event");

        $form->addDependentSelectBox('site', 'Site:', array($form['event']), function ($values) {
            $data =  new DependentSelectBoxData();
            if (isset($values['event'])) {
                $dataSite = $this->siteFacade->getNamesByEventId($values['event'],$this->locale);
                return $data->setItems($dataSite);
            }else{
                return $data;
            }
        })->setPrompt('- Select Site-')->setRequired()->setDisabledWhenEmpty(TRUE);

        $form->addMultiSelect('members','Members',$members)->setRequired(TRUE);


        $multiplier = $form->addMultiplier('multiplier', function (Nette\Forms\Container $container, Nette\Forms\Form $form) {
            $container->addDependentSelectBox('item', 'Item:', array($form['event']), function ($values) {
                $data =  new DependentSelectBoxData();
                if (isset($values['event'])) {
                    $dataItems = $this->optItemFacade->getOptItemsByEventId($values['event'],$this->locale);
                    return $data->setItems($dataItems);
                }else{
                    return $data;
                }
            })->setPrompt('-Select Item-');
            $container->addInteger('count','count');
        }, 0, 15);

        $multiplier->addCreateButton('Add');
        $multiplier->addRemoveButton('Remove');



        $form->addProtection('Security token has expired, please submit the form again');
        $form->addSubmit('send', 'Vytvořit registraci');

		$form->onSuccess[] = function (Form $form, $values) use ($onSuccess) {


            $this->registrationFacade->createRegistration($values);

			$onSuccess();
		};
		return $form;
	}

}

protected function createComponentCreateRegistrationForm($name)
    {
        $firstInput = $this->eventFacade->getNames($this->locale);
        $user = $this->userFacade->getUser($this->user->id);
        $team = $user->team;
        $members = $this->personFacade->getValidPeople($team->getId());
        $form =  $this->createRegistrationFactory->create($firstInput,$members,$this->locale,function () {
            $this->flashMessage("Registrace byla úspěšně vytvořena", 'success');
            $this->redirect(':Web:Registration:show');
        });
        $this[$name] = $form;
        return $form;
    }

@jarda256 Zítra se na to podívám. Pro usnadnění mi můžeš napsat, kde se chyba vyvolává a kdy se vyskytuje (např. po odeslání formuláře).