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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.
The input is guaranteed to be that way, there is no need to cover that case at all. If you're talking about another problem, then, that's another story.
Won't happen. There are only two possible values, there is no in between.