MultipleSelectionFormField und Dependency

<?php

namespace seo\acp\form;
use seo\data\agency\category\AgencyCategoryAction;
use seo\data\location\LocationList;
use wcf\form\AbstractFormBuilderForm;
use wcf\system\form\builder\field\BooleanFormField;
use wcf\system\form\builder\field\dependency\EmptyFormFieldDependency;
use wcf\system\form\builder\field\MultipleSelectionFormField;

/**
 * @author        Christopher Walz
 * @copyright        2017 www.cwalz.de
 */
class AgencyCategoryAddForm extends AbstractFormBuilderForm {

    /**
     * @inheritDoc
     */
    public $formAction = 'create';

    /**
     * @inheritDoc
     */
    public $objectActionClass = AgencyCategoryAction::class;

    protected function createForm() {
        parent::createForm();


        $this->form->appendChildren([
            BooleanFormField::create('special')
                ->label('seo.acp.agencyCategory.special')
                ->description('seo.acp.agencyCategory.special.description'),
            MultipleSelectionFormField::create('locations')
                ->addDependency(EmptyFormFieldDependency::create('special')
                    ->fieldId('special'))
                ->label('seo.acp.agencyCategory.locations')
                ->filterable()
                ->options(new LocationList()),
        ]);
    }
}

<?php

namespace seo\acp\form;
use seo\data\agency\category\AgencyCategory;
use wcf\system\exception\IllegalLinkException;

/**
 * @author        Christopher Walz
 * @copyright        2017 www.cwalz.de
 */
class AgencyCategoryEditForm extends AgencyCategoryAddForm {
    /**
     * @inheritDoc
     */
    public $formAction = 'update';


    /**
     * @inheritDoc
     */
    public function readParameters() {
        parent::readParameters();

        if (isset($_GET['id'])) {
            $this->formObject = new AgencyCategory($_GET['id']);

            if (!$this->formObject->categoryID) {
                throw new IllegalLinkException();
            }
        }
    }

    protected function createForm() {
        parent::createForm();

        $this->form->getNodeById('locations')->value($this->formObject->getLocationIDs());
    }
}