MODIFY: Accommodate set-unset of dns-nameserver, dns-search, hostname, h...

...ost-domain
If the function really is treated like a predicate returning truthy/falsey, the you could probably just "return ( !defined $value or $value eq '' or $value =~ /^\s*$/ )" and not bother converting to 1/0.  Thus, is becomes a one-liner if you use $$_[0] or something like that,