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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.
Sorry, asking for help is not a kata issue. You can read: https://docs.codewars.com/training/troubleshooting.
There's your answer. You tried to do
null.filter(...)
, which results in this error.Tests didn't pass. They passed until the point this error happened.
Please see https://docs.codewars.com/references/markdown/#code-block to format your code nicely and also visit https://docs.codewars.com/training/troubleshooting for general tips.