private function retrieveFormFieldDescription(AdminInterface $admin, $field)
    {
        $admin->getFormFieldDescriptions();

        $fieldDescription = $admin->getFormFieldDescription($field);

        if (!$fieldDescription) {
            throw new \RuntimeException(sprintf('The field "%s" does not exist.', $field));
        }

        if (null === $fieldDescription->getTargetEntity()) {
            throw new \RuntimeException(sprintf('No associated entity with field "%s".', $field));
        }

        return $fieldDescription;
    }