Fatal error: Uncaught Error: Class "Drupal\Core\Block\BlockBase" not found in /home/www/drupal8/test/modules/webform/src/Plugin/Block/WebformSubmissionLimitBlock.php:28 Stack trace: #0 {main} thrown in /home/www/drupal8/test/modules/webform/src/Plugin/Block/WebformSubmissionLimitBlock.php on line 28