yiisoft/yii2 — pull request #5423 by SerjRamone (2014-10-08 07:43:23+00:00)
Title: fix 'Undefined index' exception

If config behavior like that:
```php
'corsFilter' => [
'class' => Cors::className(),
'cors' => [
'Origin' => ['http://mysite.com'],
'Access-Control-Request-Headers' => ['X-Wsse'],
],
],
```
Got a exception with message 'Undefined index: Access-Control-Allow-Credentials' because the default settings will be overwritten by user's settings.