Fatal error: Uncaught Error: Class "Drupal\help\Plugin\HelpSection\HelpSectionPluginBase" not found in /home/www/drupal8/test/core/modules/help/src/Plugin/HelpSection/HookHelpSection.php:19 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/help/src/Plugin/HelpSection/HookHelpSection.php on line 19