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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.
You are importing some obscure exception class that is not part of the Java standard library. It's probably in your classpath and Eclipse picked the wrong one. The package java.lang is imported by default. If you remove the import line, then it will use java.lang.IllegalArgumentException.