raise when #{obj}_params doesn't exist

[smtlaissezfaire]

I'm having an incredibly hard time upgrading an app that was using version 2.

Can you add a mode where it raises if expose(:obj) is called without an obj_params method? Having silent failures is killer.

Obviously it would be better if this was a "compile" time error, although I understand that it would probably be much easier to implement as a run time error.