This produce a warning:

```
2023-11-19T05:33:05.421+02:00 WARN [qtp925335889-44] [puppetserver] Puppet Calling function empty() with Numeric value is deprecated. (file: /usr/local/etc/puppet/code/environments/production/modules/dns/manifests/logging/channel.pp, line: 61)
```

Since we have data-types in place (`Optional[Integer]`), we do not need
to care about an empty String.  Only `undef` will evaluate to false, and
it is the precise case we want to raise an error for.

The statistics-channels statement declares communication channels
to be used by system administrators to get access to statistics
information of the name server. BIND will only start a listener
if the directive is found in the configuration. The ACLs are
rendered similar to the `controls` directive.

Statistics are not collected on a per-zone basis by default.
To enable this behaviour, the defined type for zones has a new
parameter to do so.

This gives possibility to enable forwarding in master zone.

Add support for empty forwarders in master zone

Allows to disable forwarding in master zone to cover scenario
when server is authoritative for domain, subdomain is delegated
and global forwarding is set.