Apex domains cannot have CNAME records.
Question and response
Question
dig nexen.net. NS
Answer
nexen.net. 5 NS dns2.nexen.net.
nexen.net. 5 NS ns6.gandi.net.
nexen.net. 5 NS dns1.nexen.net.
nexen.net. 5 NS dns3.nexen.net.
Authority
The response has no authority records.
Additional
dns1.nexen.net. 5 A 89.31.149.101
dns2.nexen.net. 5 A 89.31.149.102
dns3.nexen.net. 5 A 31.15.24.33
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0