Upload of Event fails in V. 5.0.0: Error "Call to a member function txt() on null"

[DZenker]

Describe the bug
Upon uploading a new event, no upload dialogue shows up, but always an error arises. Thus, no new events can be added to an Opencast object anymore.

To Reproduce
Steps to reproduce the behavior:

1. Go to an existing Opencast repository object.
2. Click on button 'Upload Event'
3. See error "Sorry, an error occured. A logfile has been created which can be identified via the code "xxxxx_yyyy"."

Expected behavior
Upload modal dialogue should show up to upload a new event.

Log
Error thrown with message "Call to a member function txt() on null"

Stacktrace:
#13 Error in /srv/www/ilias7/ilias/Customizing/global/plugins/Services/Repository/RepositoryObject/OpenCast/src/Model/WorkflowParameter/Series/SeriesWorkflowParameterRepository.php:327
#12 srag\Plugins\Opencast\Model\WorkflowParameter\Series\SeriesWorkflowParameterRepository:buildFormSection in /srv/www/ilias7/ilias/Customizing/global/plugins/Services/Repository/RepositoryObject/OpenCast/src/Model/WorkflowParameter/Series/SeriesWorkflowParameterRepository.php:212
#11 srag\Plugins\Opencast\Model\WorkflowParameter\Series\SeriesWorkflowParameterRepository:getFormSectionForObjId in /srv/www/ilias7/ilias/Customizing/global/plugins/Services/Repository/RepositoryObject/OpenCast/src/UI/EventFormBuilder.php:194
#10 srag\Plugins\Opencast\UI\EventFormBuilder:upload in /srv/www/ilias7/ilias/Customizing/global/plugins/Services/Repository/RepositoryObject/OpenCast/classes/Event/class.xoctEventGUI.php:546
#9 xoctEventGUI:add in /srv/www/ilias7/ilias/Customizing/global/plugins/Services/Repository/RepositoryObject/OpenCast/classes/class.xoctGUI.php:46
#8 xoctGUI:performCommand in /srv/www/ilias7/ilias/Customizing/global/plugins/Services/Repository/RepositoryObject/OpenCast/classes/Event/class.xoctEventGUI.php:227
#7 xoctEventGUI:performCommand in /srv/www/ilias7/ilias/Customizing/global/plugins/Services/Repository/RepositoryObject/OpenCast/classes/Event/class.xoctEventGUI.php:199
#6 xoctEventGUI:executeCommand in /srv/www/ilias7/ilias/Services/UICore/classes/class.ilCtrl.php:217
#5 ilCtrl:forwardCommand in /srv/www/ilias7/ilias/Customizing/global/plugins/Services/Repository/RepositoryObject/OpenCast/classes/class.ilObjOpenCastGUI.php:176
#4 ilObjOpenCastGUI:executeCommand in /srv/www/ilias7/ilias/Services/UICore/classes/class.ilCtrl.php:217
#3 ilCtrl:forwardCommand in /srv/www/ilias7/ilias/Services/Repository/classes/class.ilObjPluginDispatchGUI.php:45
#2 ilObjPluginDispatchGUI:executeCommand in /srv/www/ilias7/ilias/Services/UICore/classes/class.ilCtrl.php:217
#1 ilCtrl:forwardCommand in /srv/www/ilias7/ilias/Services/UICore/classes/class.ilCtrl.php:178
#0 ilCtrl:callBaseClass in /srv/www/ilias7/ilias/ilias.php:23
...

Environment (please complete the following information):

• ILIAS version: v7.13 2022-08-31
• PHP version: 7.4.3
• Plugin version: 5.0.0
• Browser: any browser

Additional informations
Maybe somehow related to #61, but WF parameters are defined in plugin config.

[DZenker]

Implemented and tested fix 77 (#78): this solved the issue.