Follow-up from T261752.
The following request https://en.wikipedia.beta.wmcloud.org/w/api.php?action=query&format=xml&list=globalusers&gusprop=rights&gususers=CarmaHawk8294 yields the error:
<api servedby="deployment-mediawiki13">
<error code="internal_api_error_InvalidArgumentException" info="[46ead050-e738-4ac2-8fc3-36d568bbb877] Exception caught: Wikimedia\Rdbms\Platform\SQLPlatform::makeList: empty input for field ggp_group" errorclass="InvalidArgumentException" xml:space="preserve">
InvalidArgumentException at /srv/mediawiki/php-master/includes/libs/Rdbms/Platform/SQLPlatform.php(249)
from /srv/mediawiki/php-master/includes/libs/Rdbms/Platform/SQLPlatform.php(249)
#0 /srv/mediawiki/php-master/includes/libs/Rdbms/Platform/SQLPlatform.php(723): Wikimedia\Rdbms\Platform\SQLPlatform->makeList(array, int)
#1 /srv/mediawiki/php-master/includes/libs/Rdbms/Database/Database.php(3391): Wikimedia\Rdbms\Platform\SQLPlatform->selectSQLText(array, array, array, string, array, array)
#2 /srv/mediawiki/php-master/includes/libs/Rdbms/Database/DatabaseMySQL.php(665): Wikimedia\Rdbms\Database->selectSQLText(array, array, array, string, array, array)
#3 /srv/mediawiki/php-master/includes/libs/Rdbms/Database/Database.php(1360): Wikimedia\Rdbms\DatabaseMySQL->selectSQLText(array, array, array, string, array, array)
#4 /srv/mediawiki/php-master/includes/libs/Rdbms/Database/DBConnRef.php(129): Wikimedia\Rdbms\Database->select(array, array, array, string, array, array)
#5 /srv/mediawiki/php-master/includes/libs/Rdbms/Database/DBConnRef.php(386): Wikimedia\Rdbms\DBConnRef->__call(string, array)
#6 /srv/mediawiki/php-master/includes/libs/Rdbms/QueryBuilder/SelectQueryBuilder.php(761): Wikimedia\Rdbms\DBConnRef->select(array, array, array, string, array, array)
#7 /srv/mediawiki/php-master/extensions/CentralAuth/includes/Api/ApiQueryGlobalUsers.php(376): Wikimedia\Rdbms\SelectQueryBuilder->fetchResultSet()
#8 /srv/mediawiki/php-master/extensions/CentralAuth/includes/Api/ApiQueryGlobalUsers.php(177): MediaWiki\Extension\CentralAuth\Api\ApiQueryGlobalUsers->loadGroups(array, bool, bool)
#9 /srv/mediawiki/php-master/includes/Api/ApiQuery.php(735): MediaWiki\Extension\CentralAuth\Api\ApiQueryGlobalUsers->execute()
#10 /srv/mediawiki/php-master/includes/Api/ApiMain.php(2045): MediaWiki\Api\ApiQuery->execute()
#11 /srv/mediawiki/php-master/includes/Api/ApiMain.php(949): MediaWiki\Api\ApiMain->executeAction()
#12 /srv/mediawiki/php-master/includes/Api/ApiMain.php(920): MediaWiki\Api\ApiMain->executeActionWithErrorHandling()
#13 /srv/mediawiki/php-master/includes/Api/ApiEntryPoint.php(138): MediaWiki\Api\ApiMain->execute()
#14 /srv/mediawiki/php-master/includes/MediaWikiEntryPoint.php(180): MediaWiki\Api\ApiEntryPoint->execute()
#15 /srv/mediawiki/php-master/api.php(30): MediaWiki\MediaWikiEntryPoint->run()
#16 /srv/mediawiki/w/api.php(3): require(string)
#17 {main}
</error>
</api>