[LIVEINSTANCE] `$this->document` is null when it shouldn't

[csidirop]

On our demo instance TYPO3 is spamming the log with following exception:

Uncaught TYPO3 Exception: Argument 2 passed to Kitodo\Dlf\Plugin\FullTextGenerator::getDocLocalPath() must be an instance of Kitodo\Dlf\Domain\Model\Document, null given, called in /var/www/typo3/public/typo3conf/ext/dlf/Classes/Controller/PageViewController.php on line 344

For some reason the $this->document object is null when we open documents. But the document still gets loaded. This behavior does not appear in local instances.