Steps to reproduce the issue

Just installed 5.1RC1 and an extension i am working on. The Global Configuration screen has three red Notifications.

Expected result

Four green notifications.

Actual result

On green (Joola is up to date) and three red. Two work but the Unknown extensions button gives an error:

An error has occurred.

    0 Attempt to assign property "name" on null 

Call Stack
# 	Function 	Location
1 	() 	JROOT/libraries/src/Updater/Adapter/ExtensionAdapter.php:73
2 	Joomla\CMS\Updater\Adapter\ExtensionAdapter->_startElement() 	 
3 	xml_parse() 	JROOT/libraries/src/Updater/Adapter/ExtensionAdapter.php:287
4 	Joomla\CMS\Updater\Adapter\ExtensionAdapter->findUpdate() 	JROOT/libraries/src/Updater/Updater.php:263
5 	Joomla\CMS\Updater\Updater->getUpdateObjectsForSite() 	JROOT/libraries/src/Updater/Updater.php:164
6 	Joomla\CMS\Updater\Updater->findUpdates() 	JROOT/administrator/components/com_installer/src/Model/UpdateModel.php:275
7 	Joomla\Component\Installer\Administrator\Model\UpdateModel->findUpdates() 	JROOT/administrator/components/com_installer/src/Controller/UpdateController.php:113
8 	Joomla\Component\Installer\Administrator\Controller\UpdateController->find() 	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 

System information (as much as possible)

MacOS (intel), Apache, MySQL 8.0.33, PHP 8.3.1

Additional comments