我已经加载了我的会话，但它显示未定义

Question

class Googleplus extends CI_Controller {
    function __construct() {
        parent::__construct();
        $this->load->library('session');

        $this->load->helper('url');
        $this->load->library('javascript');
        $this->load->library('form_validation');
        $this->load->library('email');
    }
    public function index()
    {
        if($this->session->userdata('login') == true){
            redirect('welcome/profile');
        }
    }

当我运行我的代码时，它会显示会话错误消息：Undefined property: Googleplus::$session

文件名：controllers / Googleplus.php