Fatal error: Uncaught Error: Class "Drupal\Core\Block\BlockBase" not found in /home/www/drupal8/test/core/modules/block_content/src/Plugin/Block/BlockContentBlock.php:27 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/block_content/src/Plugin/Block/BlockContentBlock.php on line 27