Merged r9380 from trunk.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/branches/1.4-stable@9397 e93f8b46-1217-0410-a6f0-8f06a7374b81

app/models/mailer.rb

@@ -359,7 +359,7 @@ class Mailer < ActionMailer::Base
 
     issues_by_assignee = scope.all(:include => [:status, :assigned_to, :project, :tracker]).group_by(&:assigned_to)
     issues_by_assignee.each do |assignee, issues|
-      deliver_reminder(assignee, issues, days) if assignee && assignee.active?
+      deliver_reminder(assignee, issues, days) if assignee.is_a?(User) && assignee.active?
     end
   end