Fatal error: Uncaught Error: Class "Drupal\Core\Field\FieldConfigBase" not found in /home/www/drupal8/test/core/lib/Drupal/Core/Field/Entity/BaseFieldOverride.php:43 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/lib/Drupal/Core/Field/Entity/BaseFieldOverride.php on line 43