It looks like the collection.find method is looping over user-given options (including collation, if given) and applying them to the command without further checking. This means that collation will be set on the command before it even gets to the decorateWithCollation call, which furthermore implies that collation can be incorrectly passed through to the final command / decorateWithCollation is essentially not doing anything.

I noticed this when I commented out the decorateWithCollation call and no tests broke.