Yii 2.0 code: 8 是什么错误？ [ 2.0 版本 ]

{name: "PHP Notice", message: "Undefined index: ", code: 8, type: "yii\base\ErrorException",…}
code: 8
file: "D:\root\PHPTutorial\WWW\kjy\user\service\CourseService.php"
line: 193
message: "Undefined index: "
name: "PHP Notice"
stack-trace: [,…]
type: "yii\base\ErrorException"