So I tried doing that but, then tests failed because of this:
https://github.com/mozilla/addon-sdk/pull/1049/files#L3R152

The problem is `components.isSuccessCode(Cr.NS_BINDING_ABORTED)` is `false`. Of course I could modify condition on that line to ignore that specific error code, but kind of feels wrong specially since cancelling with `null` seems to work as expected.

Let me know what you think.