So this could be
```php
else {
    // try to autoload the class with an autoloader
    if (class_exists($alias, true))
          return self::$_imports[$alias]=$alias;
    else
         throw new CException(Yii::t('yii','Alias "{alias}" is invalid. Make sure it points to an existing directory.',
            array('{alias}'=>$namespace)));
}
```
Not sure which one is better. But I just found that if the class does not exists will will most likely end up with "can not include file" error by yii autoloader than the exception thrown in this place. This will happen with both solutions.