Symfony version(s) affected: 4.1 (Without Flex)

Description

After update from 4.0.11 to 4.1 error The configuration tree has no root node. is presented. Issue is mentioned in comment https://symfony.com/blog/symfony-4-1-0-released#comment-22501
How to reproduce

Update non flex symfony app to 4.1 with bundle without root node.

Additional context