Fatal error: Uncaught Error: Class "Drupal\Core\Plugin\DefaultSingleLazyPluginCollection" not found in /home/www/drupal8/test/core/modules/block/src/BlockPluginCollection.php:12 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/block/src/BlockPluginCollection.php on line 12