diff --git a/activerecord/lib/active_record/association_preload.rb b/activerecord/lib/active_record/association_preload.rb
index 61fa34a..ae064ec 100644
--- a/activerecord/lib/active_record/association_preload.rb
+++ b/activerecord/lib/active_record/association_preload.rb
@@ -220,12 +220,16 @@ module ActiveRecord
           klass_name, id_map = *klass_and_id
           klass = klass_name.constantize
 
+          # do not find if there are no ids
+          uniq_ids = id_map.keys.uniq
+          next if uniq_ids.empty?
+
           table_name = klass.quoted_table_name
           primary_key = klass.primary_key
           conditions = "#{table_name}.#{connection.quote_column_name(primary_key)} IN (?)"
           conditions << append_conditions(options, preload_options)
           column_type = klass.columns.detect{|c| c.name == primary_key}.type
-          ids = id_map.keys.uniq.map do |id|
+          ids = uniq_ids.map do |id|
             if column_type == :integer
               id.to_i
             elsif column_type == :float
diff --git a/activerecord/test/cases/associations/eager_test.rb b/activerecord/test/cases/associations/eager_test.rb
index e78624a..2072757 100644
--- a/activerecord/test/cases/associations/eager_test.rb
+++ b/activerecord/test/cases/associations/eager_test.rb
@@ -633,4 +633,17 @@ class EagerAssociationTest < ActiveRecord::TestCase
   def test_order_on_join_table_with_include_and_limit
     assert_equal 5, Developer.find(:all, :include => 'projects', :order => 'developers_projects.joined_on DESC', :limit => 5).size
   end
+
+  def test_no_null_queries
+    # has author_address and author_address_extra records
+    assert_queries(3) do
+      Author.find(1, :include => ['author_address', 'author_address_extra'])
+    end
+
+    # has no author_address or author_address_extra records
+    assert_queries(1) do #should not do 1 query per subclass
+      Author.find(2, :include => ['author_address', 'author_address_extra'])
+    end
+  end
+
 end