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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.
Returning
nilfrom a method which clearly should return eitherfalseortruecan lead to bugs. E.g.alphanumeric?(s) == falsewouldn't work as expected.But everything other than nil and false are truthy in Ruby. There's no need to do an explicit boolean conversion.