Apex domains cannot have CNAME records.
Question and response
Question
dig dnsever.org. NS
Answer
dnsever.org. 5 NS ns5.dnsever.co.uk.
dnsever.org. 5 NS ns5.dnsever.net.
dnsever.org. 5 NS ns5.dnsever.co.kr.
dnsever.org. 5 NS ns5.dnsever.com.
dnsever.org. 5 NS ns5.dnsever.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0