Perch 3 and Gallery app 2.8.8: can't delete albums and photos

Hi, I upgraded to Perch 3, which looks great, and updated the Gallery app from 2.8.6 to 2.8.8 as described on your website. Now I am not able to delete albums or photos within the albums.

When I click the "delete" button next to each album the "Are you sure?" message appears but when I click the confirmation button nothing happens and albums don't get deleted.

When I try to delete photos within an album I get this message:

Notice: Undefined index: action in /Applications/XAMPP/xamppfiles/htdocs/path-to-my-local-site/perch/addons/apps/perch_gallery/modes/images.list.pre.php on line 25

Trying to reproduce the error under different conditions, I used Perch 3 and Gallery app version 2.8.6 (I just replaced the old apps/perch_gallery folder) and I am able to delete albums and photos as normal.

This is my diagnostics report:

    Perch: 3.0, PHP: 7.0.8, MySQL: mysqlnd 5.0.12-dev - 20150407 - $Id: 241ae00989d1995ffcbbf63d579943635faf9972 $, with PDO
    Server OS: Darwin, apache2handler
    Installed apps: content (3.0), assets (3.0), categories (3.0), perch_forms (1.9), perch_gallery (2.8.8)
    App runtimes: <?php $apps_list = [ 'perch_gallery', 'perch_forms', ];
    PERCH_LOGINPATH: /perch
    PERCH_PATH: /Applications/XAMPP/xamppfiles/htdocs/sites/musicmashup/perch
    PERCH_CORE: /Applications/XAMPP/xamppfiles/htdocs/sites/musicmashup/perch/core
    PERCH_RESFILEPATH: /Applications/XAMPP/xamppfiles/htdocs/sites/musicmashup/perch/resources
    Image manipulation: GD
    PHP limits: Max upload 128M, Max POST 128M, Memory: 128M, Total max file upload: 128M
    F1: 0c66c2e1f82f9e0b7617b2cb8270f2c7
    Resource folder writeable: Yes
    HTTP_HOST: musicmashup.dev
    DOCUMENT_ROOT: /Applications/XAMPP/xamppfiles/htdocs/sites/musicmashup/
    REQUEST_URI: /perch/core/settings/diagnostics/
    SCRIPT_NAME: /perch/core/settings/diagnostics/index.php

Thanks.