Nope, take into account that that code is located in the handled_call.js file and not in the conference_group_handler.js which is the file this battery of tests is checking ;-) In the case of the conference_group_handler.js the duration is just copied since there is always one as you can see at the link I included before, this is https://github.com/mozilla-b2g/gaia/pull/18934/files#diff-8c52bec747d7922bc983df471c349280R64