| Q | A | ---------------- | ----- | Bug report? | no | Feature request? | no | BC Break report? | yes | RFC? | no | Symfony version | 3.4.x This seems to be caused by d40e7e4c2de1c4468714de8006f84aee287aace8. ``` [RuntimeException] In ArrayNodeDefinition.php line 501: ->requiresAtLeastOneElement() is not applicable to concrete nodes at path "forward.handlers" ``` My guess is that this should be a deprecation rather than an exception for 3.4.