Ensure nested preloading works when associations return nil. Closes #11145 [GMFlash]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@8894 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activerecord/CHANGELOG

@@ -1,5 +1,7 @@
 *SVN*
 
+* Ensure association preloading doesn't break when an association returns nil. ##11145 [GMFlash]
+
 * Make dynamic finders respect the :include on HasManyThrough associations.  #10998. [cpytel]
 
 * Base#instantiate_time_object only uses Time.zone when Base.time_zone_aware_attributes is true; leverages Time#time_with_datetime_fallback for readability [Geoff Buesing]

activerecord/lib/active_record/association_preload.rb

@@ -21,7 +21,7 @@ module ActiveRecord
             preload_associations(records, parent, preload_options)
             reflection = reflections[parent]
             parents = records.map {|record| record.send(reflection.name)}.flatten
-            unless parents.empty?
+            unless parents.empty? || parents.first.nil?
               parents.first.class.preload_associations(parents, child)
             end
           end

activerecord/test/cases/associations/eager_test.rb

@@ -76,6 +76,12 @@ class EagerAssociationTest < ActiveRecord::TestCase
     assert_nil Post.find(posts(:authorless).id, :include => :author).author
   end
 
+  def test_nested_loading_with_no_associations
+    assert_nothing_raised do
+      Post.find(posts(:authorless).id, :include => {:author => :author_addresss})
+    end
+  end
+
   def test_eager_association_loading_with_belongs_to_and_foreign_keys
     pets = Pet.find(:all, :include => :owner)
     assert_equal 3, pets.length