z.ns.nu has no CNAME records.
Question and response
Question
dig z.ns.nu. NS
Answer
The response has no answer records.
Authority
nu. 98 SOA catcher-in-the-rye.nic.nu. hostmaster.nic.nu. 1772701774 28800 3600 864000 7200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0