Steps to reproduce the issue

• PHP 8.1. Joomla 4.2.7
• When I open the Dashboard of a j3-4-migrated site I see fatal error:

Error: Attempt to assign property "name" on null. File: .../libraries/src/Updater/Adapter/ExtensionAdapter.php:70

When I deactivate plugin Quickicon Extension Updates error is gone.

Whatever the reason (which extension) for this error is, code inspection of the mentioned file shows a logical error. $this->currentUpdate is never defined inside switch($name) - default:, but only in switch($name) - case 'UPDATE':.

https://github.com/joomla/joomla-cms/blob/4.2-dev/libraries/src/Updater/Adapter/ExtensionAdapter.php#L53-L85

I don't know if moving this line up (before switch) is enough/correct. It helped at the moment:

$this->currentUpdate = Table::getInstance('update');