In this particular case it now seems quite obvious that these two things:
thing is a NilClass
thing is a OSX::NSCFDictionary
are not the same thing at all, and not even the same kind of thing. Obvious now and silly, but not quite so much so three levels down when I was trying to puzzle out why I could not get the fields of a hash and kept getting empty strings and harsh language about no such method for nilClass and other rubbish.
Now that I realize that I was asking the same question and getting different answers because different things are answering, I have cleared the mental block and might actually be able to finish implementing this bit of the exercise.
First though, I had a slice of yummy key lime pie. And now back into Cocoa.