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@christopherThorsen, @GarthGoldwater - Can you take a look at this?  
I chose it because the errors are more descriptive.  I asked Steiner back in July what the difference was and he advised using find_by! in most circumstances 

per Steiner - so, its generally better to use find_by! so the error is raised when you can’t find the object. which is logically when the error actually did happen