Email adress with special character in local part

I have an email adress with an umlaut in its local part: fübar@example.com and I see an 500 error page, when I try to create a user with that email.

I've seen this issue with Gitlab-CE 8.9.4

Reason was: Only able to parse up to fü):
  app/models/user.rb:769:in `new'
  app/models/user.rb:769:in `block in restricted_signup_domains'
  app/models/user.rb:766:in `each'
  app/models/user.rb:766:in `any?'
  app/models/user.rb:766:in `restricted_signup_domains'
  app/controllers/admin/users_controller.rb:105:in `block in create'
  app/controllers/admin/users_controller.rb:104:in `create'
  lib/gitlab/middleware/go.rb:16:in `call'

Update: Somebody told me the wrong email address. In fact it's really fuebar (not fübar). However, would fübar@example.com valid anyway?