When editing the list of possible values for a key/value custom field type, clicking "Add" with the field empty will lead to a HTTP 500 error from Redmine. An example stack trace is attached. The error is confirmed on current master.

It should at least be fixed that Redmine does not create an HTTP 500 error, an error message that the value must not be empty would be better.

Started POST "/custom_fields/1/enumerations" for ::1 at 2020-08-30 17:47:21 +0200
Processing by CustomFieldEnumerationsController#create as JS
  Parameters: {"utf8"=>"✓", "custom_field_enumeration"=>{"name"=>""}, "commit"=>"Add", "custom_field_id"=>"1"}
  Token Update All (2.5ms)  UPDATE `tokens` SET `tokens`.`updated_on` = '2020-08-30 17:47:21' WHERE `tokens`.`user_id` = 1 AND `tokens`.`value` = '' AND `tokens`.`action` = 'session'
   (0.3ms)  SELECT MAX(`settings`.`updated_on`) FROM `settings`
  User Load (0.3ms)  SELECT  `users`.* FROM `users` WHERE `users`.`type` IN ('User', 'AnonymousUser') AND `users`.`status` = 1 AND `users`.`id` = 1 LIMIT 1
  Current user: admin (id=1)
  CustomField Load (0.3ms)  SELECT  `custom_fields`.* FROM `custom_fields` WHERE `custom_fields`.`id` = 1 LIMIT 1
   (0.3ms)  BEGIN
   (0.2ms)  ROLLBACK
  Rendering custom_field_enumerations/create.js.erb
  Rendering custom_field_enumerations/index.html.erb
  CustomFieldEnumeration Load (0.4ms)  SELECT `custom_field_enumerations`.* FROM `custom_field_enumerations` WHERE `custom_field_enumerations`.`custom_field_id` = 1 ORDER BY `custom_field_enumerations`.`position` ASC
  Rendered custom_field_enumerations/index.html.erb (8.8ms)
  Rendered custom_field_enumerations/create.js.erb (13.7ms)
Completed 500 Internal Server Error in 100ms (ActiveRecord: 4.4ms)



ActionView::Template::Error (No route matches {:action=>"update", :controller=>"custom_field_enumerations", :custom_field_id=>"1", :id=>nil}, missing required keys: [:id]):
    14:         <%= check_box_tag "custom_field_enumerations[#{value.id}][active]", 1, value.active? %>
    15:         <%= l(:field_active) %>
    16:       
    17:       <%= delete_link custom_field_enumeration_path(@custom_field, value) %>
    18:     
    19:   <% end %>
    20:   

app/views/custom_field_enumerations/index.html.erb:17:in `block (2 levels) in _app_views_custom_field_enumerations_index_html_erb___3882666770216567044_70211539369080'
app/views/custom_field_enumerations/index.html.erb:7:in `each_with_index'
app/views/custom_field_enumerations/index.html.erb:7:in `block in _app_views_custom_field_enumerations_index_html_erb___3882666770216567044_70211539369080'
app/views/custom_field_enumerations/index.html.erb:4:in `_app_views_custom_field_enumerations_index_html_erb___3882666770216567044_70211539369080'
app/views/custom_field_enumerations/create.js.erb:1:in `_app_views_custom_field_enumerations_create_js_erb__3749928945083050900_70211553777600'
lib/redmine/sudo_mode.rb:64:in `sudo_mode'