Apex domains cannot have CNAME records.
Question and response
Question
dig theory7.net. NS
Answer
theory7.net. 5 NS dns.theory7.net.
theory7.net. 5 NS dns.theory7.nl.
theory7.net. 5 NS dns.theory7.eu.
Authority
The response has no authority records.
Additional
dns.theory7.eu. 5 A 188.245.108.163
dns.theory7.nl. 5 A 213.154.231.141
dns.theory7.net. 5 A 62.212.95.148
dns.theory7.eu. 5 AAAA 2a01:4f8:1c1e:4918:0:0:0:1
dns.theory7.nl. 5 AAAA 2001:7b8:618:a:213:154:231:141
dns.theory7.net. 5 AAAA 2001:1af8:4700:a125:22:0:0:53
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0