Configuration not using root hints, but forwarders configured later

[Grayhat]

> I think unbound has built-in hints, which it will use unless
> something else is specified. So I doubt empty file will change its
> behavior.

Yes, it does, that's why I clarified my point by posting a simple
example of an "empty" root hints file
 
> Specifying something bogus could prevent it, but local-zone as
> proposed by Yorgos seems more maintainable solution.

I'd rather use a different approach, by using NSD for the local zones
and setting up UnBound to forward to NSD for such zones AND for the
root zone at startup, then once things settle, change UnBound to use
the preferred forwarders, then as a note I prefer carrying on full
recursive resolution using UnBound and perform filtering there, instead
of relying on external DNS resolvers