RSS generation fails

Describe the bug

The application fail to generate a RSS feed on some podcasts, works on other podcasts

Steps to reproduce

1. Click on RSS button

Expected behavior

A RSS feed to be generated

Actual behavior

A page printing:

Whoops!

We seem to have hit a snag. Please try again later...

is shown and a CRITICAL error is thrown in logs

Relevant logs and/or screenshots

CRITICAL - 2021-10-24 08:56:07 --> SimpleXMLElement::addAttribute(): Argument #2 ($value) must be of type string, null given
#0 /castopod/app/Helpers/rss_helper.php(262): SimpleXMLElement->addAttribute('type', NULL)
#1 /castopod/app/Controllers/FeedController.php(50): get_rss_feed(Object(App\Entities\Podcast), '')
#2 /castopod/vendor/codeigniter4/codeigniter4/system/CodeIgniter.php(877): App\Controllers\FeedController->index('la_voix_est_lib...')
#3 /castopod/vendor/codeigniter4/codeigniter4/system/CodeIgniter.php(416): CodeIgniter\CodeIgniter->runController(Object(App\Controllers\FeedController))
#4 /castopod/vendor/codeigniter4/codeigniter4/system/CodeIgniter.php(324): CodeIgniter\CodeIgniter->handleRequest(NULL, Object(Config\Cache), false)
#5 /castopod/public/index.php(41): CodeIgniter\CodeIgniter->run()
#6 {main}

Context

• Castopod: 1.0.0-alpha.75
• OS: php8-alpine docker container (server), Manjaro (client)
• Browser: Firefox
• Web server: Nginx and PHP-FPM

Possible fixes

No idea but I can help you to investigate on this issue