Looks good! Committed to SVN. The reason this was here is because reviews used to be tied to a diff. They're not anymore, but it looks like this code was left over.
saving a draft via JSON unnecessarily requires a diff_revision field
Review Request #219 — Created Feb. 6, 2008 and submitted
I'm not sure what this diff_revision flag is used for. You go ahead and fetch the diffset using it, but then you don't actually do anything with it. I'm assuming it's not needed, but perhaps there's some subtelty I'm missing.
I've published reviews via JSON after taking this code out.