app/views/shared/metadata/edit/_lane.html.erb
<%# NOTE[xxx]: Kind of a hack because we need 'lane_metadata_attributes[lane_metadata_attributes][X]' -%>
<%= fields_for(lane) do |form| %>
<%= form.fields_for(:lane_metadata, builder: Metadata::FormBuilder) do |metadata_fields| %>
<% if @asset.external_release %>
<%= metadata_fields.select(:release_reason , [""]+Lane::LIST_REASONS_POSITIVE) %>
<% else %>
<%= metadata_fields.select(:release_reason , [""]+Lane::LIST_REASONS_NEGATIVE) %>
<% end %>
<% end %>
<% end %>