In a client project, we add the case of `result.info` being
`UException` (from `cubicweb_nemo.utils`). It resulted in a
problem, because `result.info` is `True` as boolean, but it has
no key, so it crashed. This patch does not resolve the real
problem of having a clean `info` member or knowing why it could
normally have a different type, but at least it eliminates a
problem for the final users.