On Jun 8, 9:20   ﮮ
> This is a pretty trivial error to generate. Just reference the
> constant that doesn't exist:
>
> $ irb
> ruby-1.9.2-p180 :001 > module X; module Foo; end; end
> > nil
> ruby-1.9.2-p180 :002 > X::Foo::X
> NameError: uninitialized constant X::Foo::X

Ah good point. I made an assumption. A qualifier then: X does exist.
How about this must be as top of your solution.

    module X; end