Fatal error: Uncaught Error: Class "Drupal\Core\Form\FormBase" not found in /home/fnbrshareacopy/public_html/modules/contrib/page_manager/page_manager_ui/src/Form/PageVariantAddForm.php:16 Stack trace: #0 {main} thrown in /home/fnbrshareacopy/public_html/modules/contrib/page_manager/page_manager_ui/src/Form/PageVariantAddForm.php on line 16