spf1.worldapp.com has no NS records.
NS records for this zone are defined at worldapp.com.
NS records for this zone are defined at worldapp.com.
Question and response
Question
dig spf1.worldapp.com. NS
Answer
The response has no answer records.
Authority
worldapp.com. 300 SOA ns-cloud-d1.googledomains.com. cloud-dns-hostmaster.google.com. 1 21600 3600 259200 300
Additional
. 0 OPT ; payload 512, xrcode 0, version 0, flags 0