If a TLD has a whitelist on nameservers, domains in such TLD must have
at least one nameserver. Therefore creating domains with empty nameserver
is forbidden, as well as deleting the last nameserver on a domain. We
enforce this policy by checking the number of nameservers for the new resource
to makesure it is not zero if a whitelist exists.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=127318320