Pick one of the previous challenges from the other sections or use one of the solutions of one of them, available in this repository:
Once decided, find an appropriate place in that project, to use a custom exception class.
Hint: Look for a place where you want to check for some condition that is exceptional. Maybe an argument that is passed in might be something unexpected or perhaps the result from a method or a block is unexpected. Any of these cases could be good candidates for an exception to be raised.
Once an appropriate place is found, define a custom exception to handle the unexpected behavior, customize it to your needs.
Finally, raise the exception in the correct place and rescue it.
This is an open ended challenge and there are multiple ways of solving it across different projects. The goal is to get hands-on experience when working with exceptions.