[TYPO3-mvc] Stored Domain Model within Scheduler Task is always empty

[Alfred Bez]

Hi folks,
I'm currently developing an Extbase Extension which should have a scheduler task. This scheduler task should store a domain model. A new row in the database is generated, but it's always empty (except uid and pid = 1).

Here's some code:

ext_tables.sql
############### start ##############
CREATE TABLE tx_myext_domain_model_simple (
    uid int(11) unsigned DEFAULT '0' NOT NULL auto_increment,
    pid int(11) DEFAULT '0' NOT NULL,

    titel varchar(255) DEFAULT '' NOT NULL,

    PRIMARY KEY (uid),
    KEY parent (pid),
);
############### end  ###############

Classes/Domain/Model/Simple.php
############### start ##############
<?php
namespace Vendor\Myext\Domain\Model;

use TYPO3\CMS\Extbase\DomainObject\AbstractEntity;

class Simple extends AbstractEntity {

    /**
     * Titel
     * @var string
     */
	protected $titel = '';

	public function __construct() {

	}

    public function setTitel($titel) {
        $this->titel = $titel;
    }

    public function getTitel() {
        return $this->titel;
    }

}
############### end  ###############

Classes/Domain/Repository/SimpleRepository.php
############### start ##############
<?php
namespace Vendor\Myext\Domain\Repository;

use TYPO3\CMS\Extbase\Persistence\Repository;

class SimpleRepository extends Repository {

}
############### end  ###############

Classes/Task/LoadXml.php
############### start ##############
<?php
namespace Vendor\Myext\Task;

use TYPO3\CMS\Scheduler\Task\AbstractTask;
use TYPO3\CMS\Core\Utility\GeneralUtility;
use TYPO3\CMS\Extbase\Object\ObjectManager;
use TYPO3\CMS\Extbase\Persistence\Generic\PersistenceManager;
use Vendor\Myext\Domain\Model\Simple;
use Vendor\Myext\Domain\Repository\SimpleRepository;

class LoadXml extends AbstractTask {
    public function execute() {

        $objectManager = GeneralUtility::makeInstance(ObjectManager::class);
        $persistenceManager = $objectManager->get(PersistenceManager::class);
        $simpleRepository= $objectManager->get(SimpleRepository::class);

        $simple = new Simple;
        $simple->setTitel('Titel');

        $simpleRepository->add($simple);
        $persistenceManager->persistAll();

        // send notification mail

        return true;
    }
}
############### end  ###############

A very basic mail is sent after the Model is stored.

What Am I Doing Wrong?