public static function formatEmptyIdentifier(ClassMetadata $meta)
    {
        $type = $meta->getTypeOfField(current($meta->getIdentifier()));

        switch ($type) {
            case 'bigint':
            case 'decimal':
            case 'integer':
            case 'smallint':
            case 'float':
                return 0;
            case 'guid':
                return '00000000-0000-0000-0000-000000000000';
            default:
                return '';
        }
    }