Body classes 'logged-in'/'not-logged-in' is always 'not-logged-in'

in template.php line 104
$body_classes[] = ($vars['logged_in']) ? 'logged-in' : 'not-logged-in';
is not working.
This body class is always set to 'not-logged-in'

This is probably because $vars['logged_in'] is not available by default.
we should set it manually before we can use it in $body_classes[]

should be something like:

global $user;
      // An anonymous user has a user id of zero.     
      if ($user->uid > 0) {
        // The user is logged in.
        $vars['logged_in'] = TRUE;
      }
      else {
        // The user has logged out.
        $vars['logged_in'] = FALSE;
      } 
      //before we can add it to body classes with:
      $body_classes = array();
      body_classes[] = ($vars['logged_in']) ? 'logged-in' : 'not-logged-in';