Apex domains cannot have CNAME records.
Question and response
Question
dig rev.azion.net. NS
Answer
rev.azion.net. 5 NS ns2.aziondns.com.
rev.azion.net. 5 NS ns1.aziondns.net.
rev.azion.net. 5 NS ns3.aziondns.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0