I think what partly complicates this is our 'semantic'(?) understanding of a 'user' in the context of a Rails app, where it might make more (or less) sense to r

I think what partly complicates this is our 'semantic'(?) understanding of a 'user' in the context of a Rails app, where it might make more (or less) sense to return nil, but where this is not immediately obvious. If instead you'd have a car object in the context of an app that sells junkyard items, it would make sense to return '0' instead of 'nil' when it concerns wheels (wow, this might be a terrible example...). It seems to me that using too much of this implicit 'semantic thinking' is to be avoided, especially when the semantic meaning is not entirely clear or always agreed upon, like with user objects. And if you look at this that way, it might be best to avoid returning nil in general (except perhaps for 'primitives?), and instead always go for a boolean return value. (I have little experience in these matters, so please correct me if I'm wrong!)