Fatal error: Uncaught exception 'TYPO3\CMS\Extbase\Property\Exception\InvalidSourceException' with message 'The identity property "fortbildung-klasse-programme-fuer-multiplikatoren" is no UID.' in /usr/share/php5/typo3/typo3_src-7.6.58/typo3/sysext/extbase/Classes/Property/TypeConverter/PersistentObjectConverter.php:219 Stack trace: #0 /usr/share/php5/typo3/typo3_src-7.6.58/typo3/sysext/extbase/Classes/Property/TypeConverter/PersistentObjectConverter.php(158): TYPO3\CMS\Extbase\Property\TypeConverter\PersistentObjectConverter->fetchObjectFromPersistence('fortbildung-kla...', 'PROJEKT77\\P77ve...') #1 /usr/share/php5/typo3/typo3_src-7.6.58/typo3/sysext/extbase/Classes/Property/PropertyMapper.php(199): TYPO3\CMS\Extbase\Property\TypeConverter\PersistentObjectConverter->convertFrom('fortbildung-kla...', 'PROJEKT77\\P77ve...', Array, Object(TYPO3\CMS\Extbase\Mvc\Controller\MvcPropertyMappingConfiguration)) #2 /usr/share/php5/typo3/typo3_src-7.6.58/typo3/sysext/extbase/Classes/Property/PropertyMapper.php(119): TYPO3\CMS\Extbas in /usr/share/php5/typo3/typo3_src-7.6.58/typo3/sysext/extbase/Classes/Property/PropertyMapper.php on line 128