[4.0] Argument 1 passed to Joomla\CMS\User\UserFactory::loadUserByUsername() must be of the type string

[PhilETaylor]

Steps to reproduce the issue

go to faked url:

http://127.0.0.1/administrator/index.php?option=com_messages&view=message&message_id=

same with

http://127.0.0.1/administrator/index.php?option=com_messages&view=message&layout=dasdasd

Expected result

No PHP Error. Something other than a PHP error :)

Actual result

Argument 1 passed to Joomla\CMS\User\UserFactory::loadUserByUsername() must be of the type string, null given, called in /application/libraries/src/User/User.php on line 271

[alikon]

confirmed
com_messages needs a bit of care