nil is annoying and should be avoided when possible. nil gives no useful feedback when blowing up and communicates nothing about the intent of the code. Using a Guest object is a great use of polymorphism and duck typing, which are great features of Ruby (and object orientation). Having nils all over the place and having to do `if some_obj` all of the time is messy.

Your example is pretty simple, so my solution will sound like overkill, but I would use some other type of object such as a Presenter to handle the rendering logic.