2016-07-26 15:33 GMT+02:00 Nicolai Hess <nicolaihess@gmail.com>:

Look at UndefinedObject instance side methods. You will see class hierarchy protocol. For example nil understands #subclasses message:

nil subclasses "==> {ProtoObject}"

It is true only for ProtoObject. If you will create another class with nil superclass, you will not see it here