Apex domains cannot have CNAME records.
Question and response
Question
dig professorbee.net. NS
Answer
professorbee.net. 5 NS ns-993.awsdns-60.net.
professorbee.net. 5 NS ns-702.awsdns-23.net.
professorbee.net. 5 NS ns-743.awsdns-28.net.
professorbee.net. 5 NS ns-2009.awsdns-59.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0