Fatal error: Uncaught Error: Class "Drupal\Core\Field\WidgetBase" not found in /home/www/drupal8/test/core/modules/datetime/src/Plugin/Field/FieldWidget/DateTimeWidgetBase.php:15 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/datetime/src/Plugin/Field/FieldWidget/DateTimeWidgetBase.php on line 15