Doctrine DQL error with COUNT in CASE

Repository.php

<?php

$dql = "SELECT NEW
    Acme\DomainModel\InspectionResult\ResultDetails(
      e.id, e.date,
      GroupConcat(DISTINCT e.comment),
      CASE WHEN COUNT(bps_ok.id) = 0 THEN 1 ELSE COUNT(bps_ok.id) / COUNT(DISTINCT bps_ok.id)
    )
    FROM AppBundle\Entity\Bundle e
    LEFT JOIN e.parttypeStateOk bps_ok
";    

$query = $this->_em->createQuery($dql);

Throws:
Error: Expected Doctrine\ORM\Query\Lexer::T_END, got ')'

Related:

• doctrine/orm#3764 @guilhermeblanco:
• https://groups.google.com/forum/#!topic/doctrine-user/ubapiyB6sKE
• https://groups.google.com/forum/#!topic/doctrine-user/leqU9UTC5VI
• http://stackoverflow.com/questions/32391343/case-when-not-working-doctrine2-query-builder @mjangir
• http://stackoverflow.com/questions/24568898/doctrine-2-dql-case-when-in-count @KhorneHoly

• https://twitter.com/webdevilopers/status/749356020871393282

@KhorneHoly states in his answer:
It seems like using SUM instead of COUNT will work w/ DQL.

Unfortunately this will not work for my query:
If the rows of my IDs were e.g. 2 and 3 a COUNT would correctly return 2 (rows) but SUM would return 5.