Pimcore version

11.1.4

Steps to reproduce

1. Add a PathFormatter to a relation field (I have the issue on a Many-to-Many Object Relation).
2. Open grid view for the object and add the Many-to-Many Object Relation in the grid
3. Open the Many-to-Many Object Relation in dialog

Replicated locally on the demo running 11.0.12 and on our project running 11.1.4

Actual Behavior

URL: /admin/element/get-nice-path
Method: POST
Message: Pimcore\Model\DataObject\ClassDefinition::getFieldDefinition(): Argument #1 ($key) must be of type string, null given, called in /var/www/html/vendor/pimcore/admin-ui-classic-bundle/src/Controller/Admin/ElementController.php on line 899
Trace:
in /var/www/html/vendor/pimcore/pimcore/models/DataObject/Traits/FieldDefinitionEnrichmentModelTrait.php:87
#0 /var/www/html/vendor/pimcore/admin-ui-classic-bundle/src/Controller/Admin/ElementController.php(899): Pimcore\Model\DataObject\ClassDefinition->getFieldDefinition(NULL)
#1 /var/www/html/vendor/pimcore/admin-ui-classic-bundle/src/Controller/Admin/ElementController.php(591): Pimcore\Bundle\AdminBundle\Controller\Admin\ElementController->getNicePathFormatterFieldDefinition(Object(App\Model\Product\Car), Array)
#2 /var/www/html/vendor/symfony/http-kernel/HttpKernel.php(182): Pimcore\Bundle\AdminBundle\Controller\Admin\ElementController->getNicePathAction(Object(Symfony\Component\HttpFoundation\Request))
#3 /var/www/html/vendor/symfony/http-kernel/HttpKernel.php(76): Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object(Symfony\Component\HttpFoundation\Request), 1)
#4 /var/www/html/vendor/symfony/http-kernel/Kernel.php(197): Symfony\Component\HttpKernel\HttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#5 /var/www/html/vendor/symfony/runtime/Runner/Symfony/HttpKernelRunner.php(35): Symfony\Component\HttpKernel\Kernel->handle(Object(Symfony\Component\HttpFoundation\Request))
#6 /var/www/html/vendor/autoload_runtime.php(29): Symfony\Component\Runtime\Runner\Symfony\HttpKernelRunner->run()
#7 /var/www/html/public/index.php(20): require_once('/var/www/html/v...')

Expected Behavior

On Pimcore 10.6 the dialog would open and the Many-to-Many Object Relation could be edited in dialog