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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.
Are you sure? I don't think there is any way for my code to return a None instead of a Tree. The code in the traceback is not my code, it is code from your random test generator. I do not how me creating a None tree (even if I were) would cause that error.
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