Doctrine\ORM\Exception\EntityIdentityCollisionException: While adding an entity of class KanbanBOX\Core\Card\Domain\Model\CardVersion with an ID hash of "256" to the identity map,
another object of class DoctrineProxies\__CG__\KanbanBOX\Core\Card\Domain\Model\CardVersion was already present for the same ID. This exception
is a safeguard against an internal inconsistency - IDs should uniquely map to
entity object instances. This problem may occur if:

- you use application-provided IDs and reuse ID values;
- database-provided IDs are reassigned after truncating the database without
clearing the EntityManager;
- you might have been using EntityManager#getReference() to create a reference
for a nonexistent ID that was subsequently (by the RDBMS) assigned to another
entity.

Otherwise, it might be an ORM-internal inconsistency, please report it.