AspectFactory::enrich uses 'class_uses' to check for trait, does not work for inherited classes
\TYPO3\CMS\Core\Routing\Aspect\AspectFactory::enrich uses 'class_uses' to check for trait,
but this does not work for inherited classes.
So if someone extends e.g. the PersistedJoinMapper this leads to an exception because $this->siteLanguage is not set.
A better solution would be to check if the property 'siteLanguage' exists in the object.