Error: Expected Doctrine\ORM\Query\Lexer::T_CLOSE_PARENTHESIS, got ','

Question

I am building a complex SQL query with Doctrine in SYmfony, which involves joining into multiple tables.

As part of the above SQL query, I need to use GROUP_CONCAT and hopefully I bumped on this available extension: https://github.com/beberlei/DoctrineExtensions/blob/master/lib/DoctrineExtensions/Query/Mysql/GroupConcat.php, which I put in under MyBundle\Resources\DoctrineExtensions and I also registered that in my config.yml, such as:

doctrine:
     ####
orm:
      ###
    entity_managers:
        default:

            dql:
                string_functions:
                                GROUP_CONCAT:  MyBundle\Resources\DoctrineExtensions\GroupConcat

In my class, as I initialize the extension with the following way:

    $parameterRepo  = $this->em->getRepository('MyBundle:Parameter');
    $classLoader = new \Doctrine\Common\ClassLoader('DoctrineExtensions', "MyBundle/Resources/DoctrineExtensions");
    $classLoader->register();

    $config = new \Doctrine\ORM\Configuration();
    $config->addCustomStringFunction('GROUP_CONCAT', 'MyBundle/Resources/DoctrineExtensions');

However, when I am running this query:

$qb->select("
                l.identifier,
                ct.fooName,
                ct.fooShortname,
                GROUP_CONCAT(p.field, ':', cp.parameterValue) as params,
                ct.section,
                p.field
               ")
        ->innerJoin('####')
        ->innerJoin('###')
        ->leftJoin('###')
        ->groupBy('###);

I am getting the following error:

[Syntax Error] line 0, col 167: Error: Expected Doctrine\ORM\Query\Lexer::T_CLOSE_PARENTHESIS, got ','

Is this a bug of the extension or I am missing something? How could I proceed with that? Thank you.