executeCacheQuery第一个参数想要Statement和string吗？

Using

doctrine/common                 v2.9.0
doctrine/dbal                   v2.8.0

This is the offending code part:

$qb = $db->createQueryBuilder()
    ->select(...)
    ->from(...)
    ->leftJoin(...)
    ->where(...)
    ->orderBy(...)
    ->setMaxResults(1)
    ->setParameter('forum_id', ANNOUNCEMENT_FORUM_ID ?? 3);

$query = $db->executeCacheQuery($qb->execute(), $qb->getParameters(), $qb->getParameterTypes(), new \Doctrine\DBAL\Cache\QueryCacheProfile(60, 'announcement', null));

$announcement = $query->fetch();

dump($announcement);

I'm not sure what exactly to pass as 1st Parameter for $db->executeCacheQuery(), because if i put $qb->execute() there, as it wants me to pass a Statement, i get this error:

Recoverable fatal error: Object of class PDOStatement could not be converted to string in ...../vendor/doctrine/dbal/lib/Doctrine/DBAL/Cache/QueryCacheProfile.php on line 102

Which is this part inside the QueryCacheProfile class:

When i use $qb->getSQL() instead, which is a string, i get this error:

Fatal error: Uncaught TypeError: Argument 1 passed to Doctrine\DBAL\Cache\ResultCacheStatement::__construct() must be an instance of Doctrine\DBAL\Driver\Statement, instance of PDOStatement given, called in ....

This is the doc example I followed: https://www.doctrine-project.org/projects/doctrine-dbal/en/2.8/reference/caching.html#caching

How do I manage to cache this query?