Apex domains cannot have CNAME records.
Question and response
Question
dig trulia.com. NS
Answer
trulia.com. 5 NS ns-239.awsdns-29.com.
trulia.com. 5 NS ns-1430.awsdns-50.org.
trulia.com. 5 NS ns-974.awsdns-57.net.
trulia.com. 5 NS ns-1580.awsdns-05.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0