不能在CODEIGNITER FIX ERROR中使用方法返回值

public function __construct() 
{
    parent::__construct();

    $group_data = array();
 if(empty($this->session->userdata('logged_in'))){
        $session_data = array('logged_in' => FALSE);
        $this->session->set_userdata($session_data);
    }
    else {
        $user_id = $this->session->userdata('id');
        $this->load->model('model_groups');
        $group_data = $this->model_groups->getUserGroupByUserId($user_id);

        $this->data['user_permission'] = unserialize($group_data['permission']);
        $this->permission = unserialize($group_data['permission']);
    }
}

1. 安装错误
2. CODEIGNITER MVC
3. 如何修复