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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.
Hi, Ema! I don't know if it's actual for you. But try to read the description more carefully. Parameters of function can be null and not only array.
So, first of all you need to check if any of given parameter is null.