protected function getNullForeignKeyFromRelation(string $relation): array
    {
        $key = $this->entityMap->getLocalKeys($relation);

        if (is_array($key)) {
            return $this->entityMap->getEmptyValueForLocalKey($relation);
        }

        if (is_null($key)) {
            throw new MappingException("Foreign key for relation $relation cannot be null");
        }

        return [
            $key => $this->entityMap->getEmptyValueForLocalKey($relation),
        ];
    }