This is currently blocking CI of extensions that run the WBQC phpunit test suite. Seems to be caused by a recent change in core.
Example for a failing job: https://integration.wikimedia.org/ci/job/quibble-vendor-mysql-php72-noselenium-docker/150921/console
There were 4 errors: 1) WikibaseQuality\ConstraintReport\Tests\ConstraintRepositoryLookupTest::testQueryConstraintsForExistingProperty count(): Parameter must be an array or an object that implements Countable /var/www/html/w/includes/libs/rdbms/loadbalancer/LoadBalancer.php:1506 /var/www/html/w/includes/libs/rdbms/loadbalancer/LoadBalancer.php:519 /var/www/html/w/includes/libs/rdbms/loadbalancer/LoadBalancer.php:496 /var/www/html/w/includes/libs/rdbms/loadbalancer/LoadBalancer.php:929 /var/www/html/w/includes/libs/rdbms/database/DBConnRef.php:65 /var/www/html/w/includes/libs/rdbms/database/DBConnRef.php:277 /var/www/html/w/extensions/WikibaseQualityConstraints/src/ConstraintRepositoryLookup.php:45 /var/www/html/w/extensions/WikibaseQualityConstraints/tests/phpunit/ConstraintRepositoryLookupTest.php:33 /var/www/html/w/tests/phpunit/MediaWikiIntegrationTestCase.php:467 [... 3 more similar errors]