private function isRelationForeignKeyNullable(Relation $relation)
    {
        $reflectionObj = new \ReflectionObject($relation);
        if (!$reflectionObj->hasProperty('foreignKey')) {
            return false;
        }
        $fkProp = $reflectionObj->getProperty('foreignKey');
        $fkProp->setAccessible(true);

        return isset($this->nullableColumns[$fkProp->getValue($relation)]);
    }