Fatal error: Uncaught Error: Class "Drupal\Core\Controller\ControllerBase" not found in /home/www/drupal8/test/modules/custom/my_mailer/src/Controller/MailerController.php:11 Stack trace: #0 {main} thrown in /home/www/drupal8/test/modules/custom/my_mailer/src/Controller/MailerController.php on line 11