[Here's the line that handles a null/empty return url](https://github.com/PureKrome/SimpleAuthentication/blob/35bc48b1b3f2a3b8cf5528de157974dcffb67e50/Code/Nancy.SimpleAuthentication/SimpleAuthenticationModule.cs#L164)

Remember, we do not do any redirection. we just set up the model for the consumer/developer to handle it themselves, if they want to.