Error: Attempt to read property "value" on null<br>File: /www/wwwroot/www.yuekegu.com/frontend/modules/testbank/controllers/DocpackController.php<br>Line: 257<br>Trace: #0 /www/wwwroot/www.yuekegu.com/frontend/modules/testbank/controllers/DocpackController.php(257): yii\base\ErrorHandler->handleError()
#1 [internal function]: app\modules\testbank\controllers\DocpackController->actionRelatedPackages()
#2 /www/wwwroot/www.yuekegu.com/vendor/yiisoft/yii2/base/InlineAction.php(57): call_user_func_array()
#3 /www/wwwroot/www.yuekegu.com/vendor/yiisoft/yii2/base/Controller.php(178): yii\base\InlineAction->runWithParams()
#4 /www/wwwroot/www.yuekegu.com/vendor/yiisoft/yii2/base/Module.php(552): yii\base\Controller->runAction()
#5 /www/wwwroot/www.yuekegu.com/vendor/yiisoft/yii2/web/Application.php(103): yii\base\Module->runAction()
#6 /www/wwwroot/www.yuekegu.com/vendor/yiisoft/yii2/base/Application.php(384): yii\web\Application->handleRequest()
#7 /www/wwwroot/www.yuekegu.com/frontend/web/index.php(25): yii\base\Application->run()
#8 {main}<br>