Fatal error: Uncaught Error: Interface "Drupal\Core\Session\AccountSwitcherInterface" not found in /home/www/drupal8/test/core/lib/Drupal/Core/Session/AccountSwitcher.php:12 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/lib/Drupal/Core/Session/AccountSwitcher.php on line 12