shouldnt we fix it at the Configuration level, given ->defaultValue('%kernel.project_dir%/translations')

IIUC cannotBeEmpty is missing.

shouldnt we fix it at the Configuration level, given ->defaultValue('%kernel.project_dir%/translations')

IIUC cannotBeEmpty is missing.

I see two options:

• allow null again, as it was before 3.4.x (not sure about the exact version)
• prevent null cleanly (Your suggestion is probably cleaner. Failing with a fatal php error as currently is bad.)

I am not sure which way to go. Actually it was a BC break in 3.4.x, which was not noticed quickly. For more details see #37111

i think it broke as of 4.x due the added type hint in ContainerBuilder::fileExists

before the inexistence was implicit, eg. if ($container->fileExists($dir = $defaultDir.'/'.$name)) { checks /$name at root level if $defaultDir is null.

So i think allowing explicit null in config is reasonable and should be handled as such, everywhere. As it preserves BC with 3.4

Should I add a test case checking this config value? Where should I add it? I doubt that src/Symfony/Bundle/FrameworkBundle/Tests/DependencyInjection/ConfigurationTest.php would test enough places 🤔

Thank you @SimonHeimberg.