The registrar security console failed because it assumed the email is a
required field for the registrar, but it isn't (at least - create_registrar
doesn't require an email, and update_registrar lets you remove the email).
Fixed by allowing it to *remain* unset if it was unset originally, but if it was set - it's required.
There are more fixes needed, but they aren't related to the email, so they will wait for the next CL
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=191623034
ea891001d9