Hi,

I'm trying to install the Redmine Helpdesk plugin on a Redmine 2.6 with ruby 2.2.10, but it fails.

The plugin appears correctly in the Administration -> Plugins page. However, when I try to configure the Redmine helpdesk plugin (PRO version), I get the following error:

Started GET "/settings/plugin/redmine_contacts_helpdesk" for 127.0.0.1 at 2020-05-10 13:34:54 +0200
Processing by SettingsController#plugin as HTML
  Parameters: {"id"=>"redmine_contacts_helpdesk"}
   (1.8ms)  SELECT MAX(`settings`.`updated_on`) AS max_id FROM `settings` 
  User Load (1.6ms)  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)
Completed 500 Internal Server Error in 6.0ms

NoMethodError (undefined method `plugin_redmine_contacts_helpdesk' for #<Class:0x007ffac1df3478>):
  app/controllers/settings_controller.rb:69:in `plugin'

Any idea of what is going wrong ?