FIX: missing email notifications for group mentions

app/jobs/regular/user_email.rb

@@ -57,9 +57,10 @@ module Jobs
       return skip(skip_reason) if skip_reason
 
       # Make sure that mailer exists
-      raise Discourse::InvalidParameters.new(:type) unless UserNotifications.respond_to?(args[:type])
+      raise Discourse::InvalidParameters.new("type=#{args[:type]}") unless UserNotifications.respond_to?(args[:type])
 
       message = UserNotifications.send(args[:type], @user, email_args)
+
       # Update the to address if we have a custom one
       if args[:to_address].present?
         message.to = [args[:to_address]]

app/mailers/user_notifications.rb

@@ -113,6 +113,13 @@ class UserNotifications < ActionMailer::Base
     notification_email(user, opts)
   end
 
+  def group_mentioned(user, opts)
+    opts[:allow_reply_by_email] = true
+    opts[:use_site_subject] = true
+    opts[:show_category_in_subject] = true
+    notification_email(user, opts)
+  end
+
   def user_posted(user, opts)
     opts[:allow_reply_by_email] = true
     opts[:use_site_subject] = true