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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.
If you console.log(strArr) [the split array], you can that there are empty strings in the array. Empty strings have no length and when you call an index, it will return undefined because it doesn't exist. Then you are trying to apply toUpperCase() to undefined, which returns an error because that method doesn't exist.