Kirby 2.3.0 Beta

I try this 2.3.0 beta (kirby-nightly-2.3.0-20160408155818.zip) on XAMPP (Apache/2.4.9 (Win32) PHP/5.4.27).

This code from https://getkirby.com/docs/cheatsheet/file/thumb

<?php if($user = $site->user()): ?>

<!-- some html -->

<?php if($avatar = $user->avatar()): ?>
          <?php echo $avatar->thumb([
                                      'width'   => 100, 
                                      'height'  => 100, 
                                      'quality' => 80
                                    ])->html() ?>
<?php endif; ?>

<!-- some html -->

<?php endif; ?>

fails with

Fatal error: Call to undefined method Media::thumb() in C:\xampp\htdocs\kirby_basic\site\snippets\active_user.php on line 10

if the loged in user has an avatar (*.jpg).


[Added:]

If I dump($avatar); for the user tester I get:

Media Object
(
    [url] => http://127.0.0.1:61080/kirby_basic/assets/avatars/tester.png
    [root:protected] => C:\xampp\htdocs\kirby_basic\assets\avatars\tester.png
    [filename:protected] => tester.png
    [name:protected] => tester
    [extension:protected] => png
    [content:protected] => 
    [cache:protected] => Array
        (
        )

)