Group page titles show in the navigation as None despite appearing fine in all other Doxygen parsers

[zyphlar]

We have a very large project with nested groups to organize documentation in addition to simply documenting each file or object, so when we run MkDoxy we get a nav menu stuffed full with all sorts of entries, half of which say None even though they otherwise work fine (appearing decently when clicked, showing up under Modules, etc)