Fatal error: Uncaught Error: Class "Drupal\Core\Field\FieldItemList" not found in /home/www/drupal8/test/core/modules/layout_builder/src/Field/LayoutSectionItemList.php:16 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/layout_builder/src/Field/LayoutSectionItemList.php on line 16