Apex domains cannot have CNAME records.
Question and response
Question
dig sapsf.com. NS
Answer
sapsf.com. 4 NS ns3.sap.com.
sapsf.com. 4 NS ns2.sap.de.
sapsf.com. 4 NS ns1.sap.net.
sapsf.com. 4 NS ns4.sap.asia.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0