> Apple's documentation is very clear that the presence or absence of an `NSError` does not say anything w.r.t. whether an error occurred.

Got a link handy? The doc I always refer to says (emphasis mine):

> Although Cocoa methods that indirectly return error objects in the Cocoa error domain are **guaranteed to return such objects if the method indicates failure by directly returning `nil` or `NO`**, you should always check that the return value is `nil` or `NO` before attempting to do anything with the `NSError` object.