fix case when there are no tags places on todos, the stats page would fail. Fixes #822.

Thanks Walter for finding this one

app/controllers/stats_controller.rb

@@ -652,6 +652,7 @@ class StatsController < ApplicationController
           "AND tags.id = taggings.tag_id " +
           "AND taggings.taggable_id = todos.id ", current_user.id])
     tags_ids_s = tag_ids.map(&:id).sort.join(",")
+    return {} if tags_ids_s.blank?  # return empty array for .size to work
     return Tag.find(:all, :conditions => "id in (" + tags_ids_s + ")")
   end
 

test/functional/stats_controller_test.rb

@@ -91,4 +91,20 @@ class StatsControllerTest < Test::Unit::TestCase
     assert_template "stats/show_selection_from_chart"
   end
 
+  def test_stats_render_when_tasks_have_no_taggings
+    login_as(:admin_user)
+
+    # using the default fixtures, todos have tags
+    get :index
+    assert_response :success
+
+    # clear taggings table and render again
+    taggings = Tagging.find(:all)
+    taggings.each do |t|
+      t.delete
+    end
+    get :index
+    assert_response :success
+
+  end
 end