Apex domains cannot have CNAME records.
Question and response
Question
dig spf-04.nifty.com. NS
Answer
spf-04.nifty.com. 5 NS ns-1846.awsdns-38.co.uk.
spf-04.nifty.com. 5 NS ns-1293.awsdns-33.org.
spf-04.nifty.com. 5 NS ns-438.awsdns-54.com.
spf-04.nifty.com. 5 NS ns-668.awsdns-19.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0