Apex domains cannot have CNAME records.
Question and response
Question
dig SUB0.135.245.119.in-addr.arpa. NS
Answer
SUB0.135.245.119.in-addr.arpa. 5 NS ns.dicey.org.
SUB0.135.245.119.in-addr.arpa. 5 NS ns2.sphere.ad.jp.
Authority
The response has no authority records.
Additional
ns2.sphere.ad.jp. 5 A 202.239.113.26
ns2.sphere.ad.jp. 5 AAAA 2001:2c0:11:1:0:0:0:a02
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0