Index: app/models/issue.rb
===================================================================
--- app/models/issue.rb	(revision 12072)
+++ app/models/issue.rb	(working copy)
@@ -108,10 +108,10 @@
         when 'all'
           nil
         when 'default'
-          user_ids = [user.id] + user.groups.map(&:id)
+          user_ids = [user.id] + user.groups.map(&:id).reject(&:nil?)
           "(#{table_name}.is_private = #{connection.quoted_false} OR #{table_name}.author_id = #{user.id} OR #{table_name}.assigned_to_id IN (#{user_ids.join(',')}))"
         when 'own'
-          user_ids = [user.id] + user.groups.map(&:id)
+          user_ids = [user.id] + user.groups.map(&:id).reject(&:nil?)
           "(#{table_name}.author_id = #{user.id} OR #{table_name}.assigned_to_id IN (#{user_ids.join(',')}))"
         else
           '1=0'