TYPO3: Login-attempt with an empty password!

php7.4-fpm stderr | PHP message: TYPO3 [WARNING] request="ae37a1b8a44f6" component="TYPO3.CMS.Core.Authentication.AuthenticationService": Login-attempt from 172.17.0.1, for username 'cweiske' with an empty password! "

Happened when moving a TYPO3 v9 to a composer-based installation. Flushing the cache in the install tool helped.