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Collections are a way for you to organize kata so that you can create your own training routines. Every collection you create is public and automatically sharable with other warriors. After you have added a few kata to a collection you and others can train on the kata contained within the collection.
Get started now by creating a new collection.
If I saw this in a codebase I would hunt you down and beat you about the head for making me think so hard as to what this does. This isn't a good code golf solution either as it's longer than several other solutions. interesting use of filter though!
Technically
scould also be null so I checked for both situations in my attempt