Noticed this in our travis jobs.
PHP Catchable fatal error: Object of class PDO could not be converted to string in /home/travis/build/wikimedia/phase3/includes/db/Database.php on line 4201 PHP Stack trace: PHP 1. {main}() /home/travis/build/wikimedia/phase3/maintenance/install.php:0 PHP 2. require_once() /home/travis/build/wikimedia/phase3/maintenance/install.php:158 PHP 3. CommandLineInstaller->execute() /home/travis/build/wikimedia/phase3/maintenance/doMaintenance.php:103 PHP 4. CliInstaller->execute() /home/travis/build/wikimedia/phase3/maintenance/install.php:144 PHP 5. Installer->performInstallation() /home/travis/build/wikimedia/phase3/includes/installer/CliInstaller.php:135 PHP 6. call_user_func:{/home/travis/build/wikimedia/phase3/includes/installer/Installer.php:1596}() /home/travis/build/wikimedia/phase3/includes/installer/Installer.php:1596 PHP 7. Installer->createMainpage() /home/travis/build/wikimedia/phase3/includes/installer/Installer.php:1596 PHP 8. WikiPage->doEditContent() /home/travis/build/wikimedia/phase3/includes/installer/Installer.php:1751 PHP 9. WikiPage->doEditUpdates() /home/travis/build/wikimedia/phase3/includes/page/WikiPage.php:1939 PHP 10. ParserCache->save() /home/travis/build/wikimedia/phase3/includes/page/WikiPage.php:2172 PHP 11. SqlBagOStuff->set() /home/travis/build/wikimedia/phase3/includes/parser/ParserCache.php:288 PHP 12. SqlBagOStuff->setMulti() /home/travis/build/wikimedia/phase3/includes/objectcache/SqlBagOStuff.php:357 PHP 13. SqlBagOStuff->garbageCollect() /home/travis/build/wikimedia/phase3/includes/objectcache/SqlBagOStuff.php:298 PHP 14. SqlBagOStuff->expireAll() /home/travis/build/wikimedia/phase3/includes/objectcache/SqlBagOStuff.php:518 PHP 15. SqlBagOStuff->deleteObjectsExpiringBefore() /home/travis/build/wikimedia/phase3/includes/objectcache/SqlBagOStuff.php:523 PHP 16. SqlBagOStuff->getDB() /home/travis/build/wikimedia/phase3/includes/objectcache/SqlBagOStuff.php:535 PHP 17. sprintf() /home/travis/build/wikimedia/phase3/includes/objectcache/SqlBagOStuff.php:171 PHP 18. DatabaseBase->__toString() /home/travis/build/wikimedia/phase3/includes/objectcache/SqlBagOStuff.php:171