nutzung der Doctrine Extension ifnull

hallo leutz, kann mir jemand von euch kurz erklären, wie ich die DoctrineExtensions\Query\Mysql\IfNull in meiner query nutzen kann? $builder = Shopware()-\>Models()-\>createQueryBuilder(); $builder-\>select(array('articles', 'attributes', 'details', 'prices', 'category')); $builder-\>from('Shopware\Models\Article\Article', 'articles'); $builder-\>leftJoin('articles.attribute', 'attributes'); $builder-\>leftJoin('articles.details', 'details'); $builder-\>leftJoin('details.prices', 'prices'); $builder-\>leftJoin('articles.categories', 'category'); $builder-\>where('category.id IN ('.implode(',', $categories).')'); $builder-\>addGroupBy('articles.id'); $builder-\>setFirstResult($start); $builder-\>setMaxResults($limit); $query = $builder-\>getQuery();