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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.
Just a thought with these challenges, I try to look at how they are explicitly written and go from there - Most of the time they will say what data type the input is, allowing for you to make the assumption that the input is a certain data type (array in this case) and therefore you do not have to check the input.
I see what you are doing and why, just thought I'd share my take on it