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This pull-request has been approved by: brendandburns

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@brendanburns My biggest concern is that the test coverage doesn't feel enough for all the defensive checks that were added?

But other wise the good looks good.

@drubin actually, I had a bug in some of the defensive stuff and it lit the tests up pretty good :)

But I'm happy to add further tests specific to that code if you'd prefer.

/lgtm

@brendanburns It was just a feeling but I didn't look at the rest of the existing tests so happy to defer to your judgement here.