Fatal error: Uncaught Error: Class 'Drupal\Core\Form\FormBase' not found in /var/www/html/tmp/contrib/mimemail/modules/mimemail_example/src/Form/ExampleForm.php:16 Stack trace: #0 {main} thrown in /var/www/html/tmp/contrib/mimemail/modules/mimemail_example/src/Form/ExampleForm.php on line 16