Fatal error: Uncaught Error: Class "Drupal\Component\Plugin\PluginBase" not found in /home/www/drupal8/test/core/lib/Drupal/Core/Menu/LocalTaskDefault.php:15
Stack trace:
#0 {main}
thrown in /home/www/drupal8/test/core/lib/Drupal/Core/Menu/LocalTaskDefault.php on line 15