<%= fields_for "external_domains[#{blank_external_domain.to_param}]", blank_external_domain do |external_domain_form| %>
<% end %>
<% @form.external_domains.each do |external_domain| %>
<%= fields_for "external_domains[]", external_domain do |external_domain_form| %>
<%= render "external_domain",
form: external_domain_form,
id: external_domain.to_param %>
<% end %>
<% end %>