Loading collection data...
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.
Your solution is correct and does not cause such error for me. Maybe you have modified the content of "Sample tests" box? Try to reset the trainer (backup your solution first!) and see if problem still persists.