Google Code-in

In MediaWiki core, the file includes/installer/Installer.php has references to an old debugging variable $this->debug (around line 697). Since this debugging system has been removed, remove all remaining references to it.

Additionally the old debugging system was outputting exceptions in unescaped ways, so may have been unsafe from an XSS perspective, so all the more reason to get rid of it.

You are expected to provide a patch in Wikimedia Gerrit. See https://www.mediawiki.org/wiki/Gerrit/Tutorial for how to set up Git and Gerrit.