Apex domains cannot have CNAME records.
Question and response
Question
dig xunurl.com. NS
Answer
xunurl.com. 5 NS n1.xundns.com.
xunurl.com. 5 NS n2.xundns.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0