Fatal error: Uncaught Error: Class 'yii\helpers\StringHelper' not found in /opt/lampp/htdocs/io.core.websocket/vendor/yiisoft/yii2-gii/src/generators/crud/default/views/index.php:9 Stack trace: #0 {main} thrown in /opt/lampp/htdocs/io.core.websocket/vendor/yiisoft/yii2-gii/src/generators/crud/default/views/index.php on line 9