RequestFactory throws Exception when returning an entity with a null Proxy relationship

I have an entity that has an optional entity that is specified in the with() method of the call (e.g. bookRequest().findByDate(date).with("author")).  When author is null, it throws an exception.  Is this the expected behavior?  Is there any way to return an object with an optional relationship?

Stacktrace: 

http://pastebin.com/y80E2GMT

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