Apex domains cannot have CNAME records.
Question and response
Question
dig plma.se. NS
Answer
plma.se. 5 NS dns10.telia.com.
plma.se. 5 NS dns11.se.telia.net.
plma.se. 5 NS dns12.se.telia.net.
plma.se. 5 NS dns9.telia.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0