public function findByIdentifier($identifier)
    {
        $object = $this->persistenceManager->getObjectByIdentifier($identifier, $this->entityClassName);
        if ($object === null) {
            foreach ($this->addedResources as $addedResource) {
                if ($this->persistenceManager->getIdentifierByObject($addedResource) === $identifier) {
                    $object = $addedResource;
                    break;
                }
            }
        }

        return $object;
    }