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" tocomposer.json
• changeextra.symfony.require to^4.2 incomposer.json
• composer update

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

Possible Solution

Additional context