Call to a member function assign() on null on new user submision

Hello
after an upragde from joomla 3.1 to joomla 5.13 - PHP 8.3 (I allready do that with me 2 others sites without any problem) there is this error message when a new usre try to register: Call to a member function assign() on null 
the new user was created on joomla but not on CB.
How can i fix that?
Best regards
 

Enable debug mode and maximum error reporting in Joomla global configuration then retry. That should expose the rest of the error so we can see where it's coming from.

I have the same error so looking forward to any fix.

 

I have the same error so looking forward to any fix.

Please follow the instructions of my reply above and provide the details of the error. As the original poster has not done so there's nothing for me to investigate and fix.

Same issue overhere,I guess the plugin DPcalender causes the error? No Idea why its called when adding a new Joomla user.
see error output below:

   0 Call to a member function assign() on null

Call Stack
#     Function     Location
1     ()     JROOT/plugins/user/dpcalendar/src/Extension/DPCalendar.php:101
2     DigitalPeak\Plugin\User\DPCalendar\Extension\DPCalendar->onUserAfterSave()     JROOT/libraries/src/Plugin/CMSPlugin.php:289
3     Joomla\CMS\Plugin\CMSPlugin->Joomla\CMS\Plugin\{closure}()     JROOT/libraries/vendor/joomla/event/src/Dispatcher.php:454
4     Joomla\Event\Dispatcher->dispatch()     JROOT/libraries/src/User/User.php:803
5     Joomla\CMS\User\User->save()     JROOT/administrator/components/com_users/src/Model/UserModel.php:288
6     Joomla\Component\Users\Administrator\Model\UserModel->save()     JROOT/libraries/src/MVC/Controller/FormController.php:689
7     Joomla\CMS\MVC\Controller\FormController->save()     JROOT/administrator/components/com_users/src/Controller/UserController.php:105
8     Joomla\Component\Users\Administrator\Controller\UserController->save()     JROOT/libraries/src/MVC/Controller/BaseController.php:730
9     Joomla\CMS\MVC\Controller\BaseController->execute()     JROOT/libraries/src/Dispatcher/ComponentDispatcher.php:143
10     Joomla\CMS\Dispatcher\ComponentDispatcher->dispatch()     JROOT/libraries/src/Component/ComponentHelper.php:361
11     Joomla\CMS\Component\ComponentHelper::renderComponent()     JROOT/libraries/src/Application/AdministratorApplication.php:150
12     Joomla\CMS\Application\AdministratorApplication->dispatch()     JROOT/libraries/src/Application/AdministratorApplication.php:195
13     Joomla\CMS\Application\AdministratorApplication->doExecute()     JROOT/libraries/src/Application/CMSApplication.php:306
14     Joomla\CMS\Application\CMSApplication->execute()     JROOT/administrator/includes/app.php:58
15     require_once()     JROOT/administrator/index.php:32

 

Yup, your issue is coming from 3rd party plugin DPcalender acting on Joomla user save event causing a fatal error that's interrupting the process so CB can't create its user. Suggest contacting the developers of DPcalender and have them fix the issue.