警告：session_destroy（）：尝试在第27行的D：\ xampp \ htdocs \ PHP \ MyBlog \ lib \ Session.php中销毁未初始化的会话

when i try include with ../ at that time this error showing me.
Warning: session_destroy(): Trying to destroy uninitialized session in D:\xampp\htdocs\PHP\MyBlog\lib\Session.php on line 27

Admin login file location MyBlog/admin/inc/header.php

  <?php 
        include '../lib/Session.php';
        Session::checkSession();    
        if (isset($_GET['action']) && $_GET['action'] == "logout"){
            Session::destroy();
        }
    ?>
<li><a href="?action=logout">Logout</a></li>

My Session File location MyBlog/lib/Session.php

<?php 
    class Session{
        public static function init(){
            session_start();
        }

        public static function set($key, $val){
            $_SESSION['$key'] = $val;
        }

        public static function get($key){

            if(isset($_SESSION['$key'])){
                return $_SESSION['$key'];
            } else{
                return false;
            }
        }
        public static function checkSession(){
            self::init();
            if(self::get("login")==false){
                self::destroy();
            header("Locaton:login.php");
            }
        }
        public static function destroy(){
            session_destroy();
            header("Locaton:login.php");
        }
    }
?>

Then i also try this :

 <?php 
    // include  ($_SERVER['DOCUMENT_ROOT'].'/lib/Session.php');
    //include "../../lib/Session.php";
    include "/lib/Session.php";
    Session::checkSession();    
?>

Then its showing this kind of error: Warning: include(/lib/Session.php): failed to open stream: No such file or directory in D:\xampp\htdocs\PHP\MyBlog\admin\inc\header.php on line 4