PHP session notice:undefined index : I am trying to pass a value using session from one page to another but it says 

> Notice: Undefined index: user_id in path\file.php on line 61

The file where i am creating session is as follows


     if(!isset($_SESSION)) 
        { 
            session_start(); 
        } 
then

     $_session['user_id']=$row['user_id'];

The file i am receiving session is as follows

    if(!isset($_SESSION)) 
        { 
            session_start(); 
        } 
then

    $user_id=$_session['user_id'];

Where i am making mistake. Kindly guide me please