TYPO3 Core

I used the following csp.yaml in my site:

inheritDefault: true
mutations:
  # Results in `default-src 'self'`
  - mode: set
    directive: 'default-src'
    sources:
      - "'self'" 

  # Results in `'unsafe-inline' https://piwik.example.org/  https://service.example.org/
  - mode: extend
    directive: 'unsafe-inline'
    sources:
      - 'https://piwik.example.org/'
      - 'https://service.example.org/'

When I then try to display the frontend I get

(1/1) TypeError
TYPO3\CMS\Core\Security\ContentSecurityPolicy\Mutation::__construct(): Argument #2 ($directive) must be of type TYPO3\CMS\Core\Security\ContentSecurityPolicy\Directive, null given, called in /var/www/html/vendor/typo3/cms-core/Classes/Security/ContentSecurityPolicy/ModelService.php on line 63

The example configuration https://docs.typo3.org/m/typo3/reference-coreapi/12.4/en-us/ApiOverview/ContentSecurityPolicy/Index.html#site-specific-frontend does not cause this error.