Reproducer: https://github.com/theofidry/bug-9283

composer install
docker-compose up -d
bin/console doctrine:migration:migrate --env test
vendor/bin/phpunit

We have been using API-Platform with VOs as entity identifiers. Although the doc generated by API-Platform looks wrong (assumes it's an object):

It is in practice working fine.

However when it comes to the testing utilities, the ::assertMatchesResource{Item,Collection}JsonSchema() assertions now fail with a message along the lines of:

hydra:member[0].id: Integer value found, but an object is required