Refactor book_detail view to use Book object.  Include alternative titles in book_detail view.

If I'm understanding this right - here a Book object is returned, with no data. Line 69 in get_or_404 looks at that object & checks for it's truth value. The value is false, because of the __nonzero__ method in BDRObject that checks for data. Is that correct? If so, why not return None on this line, and remove the __nonzero__ method in BDRObject? Seems like that would be simpler, unless this is required for another reason...