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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.
aandbcan be null (None). Null values don't, and can't, have attributes. The error messages says this loud and clear. Try troubleshooting your solution. There is documentation for this.Same issue here.