Symfony version(s) affected: 4.3.0-BETA1, 4.4.0-dev

Description
When running the latest dev code, a 500 error is thrown in /_wdt/{identifier}.

How to reproduce

• composer create-project symfony/website-skeleton
• add "minimum-stability": "beta" to composer.json
• change extra.symfony.require to ^4.2 in composer.json
• composer update

See reproducer app here: https://github.com/j4nr6n/reproducerApp

Possible Solution

Additional context