Custom Export Plugin: Error when exporting. OJS

More Info on what I did below.
I am receiving the following error when trying to run a custom export plugin, which is a 99% clone of the native importexport plugin:

[Tue Jun 07 14:10:58.996548 2022] [php7:notice] [pid 1572] [client ...] PHP Notice:  Undefined property: ArticleLZAXmlFilter::$parent in /var/www/ojs_bibliometrie/plugins/importexport/LZA_export/filter/ on line 64, referer: .../management/importexport/plugin/LZAExportPlugin
[Tue Jun 07 14:10:58.996649 2022] [php7:error] [pid 1572] [client ...] PHP Fatal error:  Uncaught Error: Class name must be a valid object or a string in /var/www/ojs_bibliometrie/plugins/importexport/LZA_export/filter/
Stack trace:
#0 /var/www/ojs_bibliometrie/lib/pkp/plugins/importexport/native/filter/ ArticleLZAXmlFilter->createSubmissionNode(Object(DOMDocument), Object(Submission))
#1 /var/www/ojs_bibliometrie/lib/pkp/classes/filter/ SubmissionNativeXmlFilter->process(Array)
#2 /var/www/ojs_bibliometrie/plugins/importexport/LZA_export/ Filter->execute(Array, true)
#3 /var/www/ojs_bibliometrie/plugins/importexport/LZA_export/ LZAExportPlugin->exportSubmissions(Array, Object(Journal), Object(User))
#4 /var/www/ojs_bibliometrie/lib/pkp/pages/management/ LZAExportPlugin->display(Array, Object(Request))
#5 /var/www/ojs_bibliometrie/lib/pkp/classes/core/ PKPToolsHandler->importexport(Array, Object(Request in /var/www/ojs_bibliometrie/plugins/importexport/LZA_export/filter/ on line 64, referer: .../management/importexport/plugin/LZAExportPlugin

After searching through the Stacktrace and finding no source of the error, maybe the Undefined property: ArticleLZAXmlFilter::$parent is the problem?

the constructor in this class seems correct though:


class ArticleLZAXmlFilter extends SubmissionNativeXmlFilter {
	 * Constructor
	 * @param $filterGroup FilterGroup
	function __construct($filterGroup) {

More Info:

As described in an earlier thread: OJS 3.3 registering additional filters for XML Export - #10 by KBodarwe
I’m working on an extension to the native import-export Plugin.
The requirements are as follows:

  • Able to export single Articles as XML.
  • Have all files attached to the Article (including review etc.) in the XML.
  • Have conversations linked to the Article in the XML.

To do this, I have copied the native import-export plugin and renamed everything to suit my project.
I have registered the needed filters in the ‘filters’ and ‘filter_groups’ in the database.

Only parts I have changed are parts of the code that are filtering out unwanted files, in an attempt to receive all files:

function addFiles($doc, $submissionNode, $submission) {

This function is usually in plugins/importexport/native/filter/

I have instead defined this in which is a clone of plugins/importexport/native/filter/ and a direct child of SubmissionNativeXmlFilter.

Any help on this would be greatly appreciated as I’m working on this for quite a while now without progress.
Best Regards,