Apex domains cannot have CNAME records.
Question and response
Question
dig yale.edu. NS
Answer
yale.edu. 1 NS ns1.bluecatdns.org.
yale.edu. 1 NS ns1.bluecatdns.com.
yale.edu. 1 NS PKS1302-102.net.yale.edu.
yale.edu. 1 NS PKS1302-103.net.yale.edu.
yale.edu. 1 NS ns1.bluecatdns.net.
Authority
The response has no authority records.
Additional
ns1.bluecatdns.com. 3 A 162.159.11.78
ns1.bluecatdns.net. 3 A 162.159.9.100
ns1.bluecatdns.org. 3 A 162.159.10.254
pks1302-102.net.yale.edu. 1 A 128.36.72.27
pks1302-103.net.yale.edu. 1 A 128.36.72.29
ns1.bluecatdns.com. 3 AAAA 2400:cb00:2049:1:0:0:a29f:b4e
ns1.bluecatdns.net. 3 AAAA 2400:cb00:2049:1:0:0:a29f:964
ns1.bluecatdns.org. 3 AAAA 2400:cb00:2049:1:0:0:a29f:afe
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0