Fatal error: Uncaught Error: Class 'yii\helpers\StringHelper' not found in /mnt/www/service_center/vendor/yiisoft/yii2-gii/generators/crud/default/controller.php:13 Stack trace: #0 {main} thrown in /mnt/www/service_center/vendor/yiisoft/yii2-gii/generators/crud/default/controller.php on line 13