Apex domains cannot have CNAME records.
Question and response
Question
dig 10-19.124.242.130.in-addr.arpa. NS
Answer
10-19.124.242.130.in-addr.arpa. 5 NS b.ns.kth.se.
10-19.124.242.130.in-addr.arpa. 5 NS a.ns.kth.se.
Authority
The response has no authority records.
Additional
a.ns.kth.se. 5 A 130.237.72.246
b.ns.kth.se. 5 A 130.237.72.250
a.ns.kth.se. 5 AAAA 2001:6b0:1:0:0:0:0:246
b.ns.kth.se. 5 AAAA 2001:6b0:1:0:0:0:0:250
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0