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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.
OP solved it, closing
description updated
Ah I think you were hitting the same problem as me! I also did a solution involving MUTATING the loop nodes. The rather unhelpful error message is coming from a test which calls your function TWICE on the same loop... now you know this you should be able to fix it!