When you are using non-Active Directory-integrated DNS, you cannot reload a zone that contains reserved words:
NOTE: If you create a zone with reserved words, it ceases to function when DNS is restarted.
To workaround this feature, use the DNSCMD utility to create the zone using a new name:
DNSCMD /ZONEADD nul.com /Primary /File nulinc.com.dns
NOTE: Zone files are named after the zone. Upper case is NOT permitted.