Native XML export - Trying to get property of non-object

We have an issue related to Native XML export

For a journal we still use OJS 3.0.2 and we want to export all articles. After making some modifications to the templates suggested here pkp/pkp-lib#1709 consider query files and source attribute, and use the same file id for all revisions imports by bozana · Pull Request #2311 · pkp/pkp-lib · GitHub it was possible to export all files, except for one document. I end up with this error

Warning: file_get_contents(/srv/www/ojs/upload/journals/3//articles/81/submission/review/81-25-346-1-4-20180516.docx): failed to open stream: Datei oder Verzeichnis nicht gefunden in /srv/www/ojs/ojs/lib/pkp/plugins/importexport/native/filter/SubmissionFileNativeXmlFilter.inc.php on line 120

Notice: Trying to get property of non-object in /srv/www/ojs/ojs/lib/pkp/plugins/importexport/native/filter/SubmissionNativeXmlFilter.inc.php on line 284

Fatal error: Call to a member function getAttribute() on a non-object in /srv/www/ojs/ojs/lib/pkp/plugins/importexport/native/filter/SubmissionNativeXmlFilter.inc.php on line 284

So, I created the “missing” files (it seems, that the file was once uploaded in the review process, but deleted later).

Now, I still get this error message

Notice: Trying to get property of non-object in /srv/www/ojs/ojs/lib/pkp/plugins/importexport/native/filter/SubmissionNativeXmlFilter.inc.php on line 284

Fatal error: Call to a member function getAttribute() on a non-object in /srv/www/ojs/ojs/lib/pkp/plugins/importexport/native/filter/SubmissionNativeXmlFilter.inc.php on line 284

I assume, that there’s still a file missing or an entry in a table, but I don’t know, where I have to look.