What happened?

Description

Spotted this when working on different feature branches, so an edge case perhaps.

Steps to reproduce

1. Create a new branch with a new user group.
2. Create a new user group and assign a user to that group (and that group only).
3. Switch to a different branch and run project config migration.

At this point, the following error is thrown in the console:

error: Cannot assign null to property craft\events\UserGroupEvent::$userGroup of type craft\models\UserGroup
Failed to run craft up: exit status 1

Expected behavior

User group can be removed from project config without error.

Actual behavior

Migration fails where users are assigned solely to the removed group.

Craft CMS version

4.10.5

PHP version

8.2.18

Operating system and version

No response

Database type and version

No response

Image driver and version

No response

Installed plugins and versions