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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.
expected:<[]>looks appropriate.was:<[null]>looks like a problem in your code.I suggest printing the data entering your function and the data you return in a way that doesn't get crumbled by HTML nature of CodeWars console.