Apex domains cannot have CNAME records.
Question and response
Question
dig tele2.se. NS
Answer
tele2.se. 5 NS ystad.dns.swip.net.
tele2.se. 5 NS sunic.sunet.se.
tele2.se. 5 NS c.dns.tele2.net.
tele2.se. 5 NS pitea.dns.swip.net.
Authority
The response has no authority records.
Additional
c.dns.tele2.net. 5 A 130.242.124.20
sunic.sunet.se. 5 A 192.36.125.2
c.dns.tele2.net. 5 AAAA 2001:6b0:7:124:0:0:0:20
sunic.sunet.se. 5 AAAA 2001:6b0:7:0:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0