There are a few `!= undefined` in the code (I’d prefer to have `!== undefined` instead…) but they make sense: a setting can be set to false, which is different from undefined (= not set).

This `!= 'undefined'` here is intentional. It has been added because of bug 880617, see #10676. In retrospect I think I should have asked for a more specific test (= restricted to the `deviceinfo.mac` setting) and to leave a comment mentioning bug 880617.