This code looks broken to me;
$this->allPreferences = Preferences::getPreferences( $this->getUser(), $this->getContext() );
found in includes/specials/SpecialPreferencesList.php. There is no such class as Preferences in this code base but only PreferencesListPreferences class exists with a getPreferences() definition.
Also, I see that calls to getPreferences() have been made in other places with;
$thisUsersPreferences = PreferencesListPreferences::getPreferences( $user, $preferenceNames, $context );
Noticed after submitting: https://gerrit.wikimedia.org/r/c/mediawiki/extensions/PreferencesList/+/514112 which caused this failure: https://integration.wikimedia.org/ci/job/quibble-vendor-mysql-hhvm-docker/51671/console.