Error CSS must be nested under a category

Replicate error:
- Enable yasm module
- Go to /admin/reports/yasm

Then the error will pop-up:
Error: The website encountered an unexpected error. Please try again later.
AssertionError: CSS must be nested under a category. See https://www.drupal.org/node/2274843 → . in assert() (line 133 of core/lib/Drupal/Core/Asset/LibraryDiscoveryParser.php).

I think this is because at the file yasm.libraries.yml at line 5 (assets/css/yasm.css) you need to add {} at the end, like: "assets/css/yasm.css: {}"