[web-devel] [Yesod] What is ContentFile's second argument?

Hi Now, I'm converting my yesod app 0.7 to 0.8 I'm facing to the code like this. return $ RepHtml $ ContentFile path I looked up ContentFile has 2 arguments, on 0.8. the second argument of this is Maybe FilePart. If I write this Nothing, what does it mean? thanks.