Apex domains cannot have CNAME records.
Question and response
Question
dig checkpoint-spf.com. NS
Answer
checkpoint-spf.com. 5 NS ns-843.awsdns-41.net.
checkpoint-spf.com. 5 NS ns-1356.awsdns-41.org.
checkpoint-spf.com. 5 NS ns-1686.awsdns-18.co.uk.
checkpoint-spf.com. 5 NS ns-42.awsdns-05.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0