Apex domains cannot have CNAME records.
Question and response
Question
dig nic.se. NS
Answer
nic.se. 5 NS nsa.dnsnode.net.
nic.se. 5 NS nsu.dnsnode.net.
nic.se. 5 NS nsp.dnsnode.net.
Authority
The response has no authority records.
Additional
nsa.dnsnode.net. 1 A 194.58.192.46
nsp.dnsnode.net. 1 A 194.58.198.32
nsu.dnsnode.net. 1 A 185.42.137.98
nsa.dnsnode.net. 1 AAAA 2a01:3f1:46:0:0:0:0:53
nsp.dnsnode.net. 1 AAAA 2a01:3f1:3032:0:0:0:0:53
nsu.dnsnode.net. 1 AAAA 2a01:3f0:400:0:0:0:0:32
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0