Apex domains cannot have CNAME records.
Question and response
Question
dig space. NS
Answer
space. 5 NS ns01.trs-dns.com.
space. 5 NS ns01.trs-dns.net.
space. 5 NS ns10.trs-dns.org.
space. 5 NS ns10.trs-dns.info.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0