Apex domains cannot have CNAME records.
Question and response
Question
dig saas.zenoss.com. NS
Answer
saas.zenoss.com. 4 NS ns-1229.awsdns-25.org.
saas.zenoss.com. 4 NS ns-1828.awsdns-36.co.uk.
saas.zenoss.com. 4 NS ns-11.awsdns-01.com.
saas.zenoss.com. 4 NS ns-971.awsdns-57.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0