From 21750122308a38cd2eaf9b46aa1789966eb8abd9 Mon Sep 17 00:00:00 2001
From: Georg Friedrich <georg@wobolando.com>
Date: Mon, 5 Sep 2011 21:25:57 +1000
Subject: [PATCH] Don't find belongs_to target when the foreign_key is NULL.
 Fixes #2828

---
 .../active_record/associations/belongs_to_association.rb    | 4 ++++
 .../test/cases/associations/belongs_to_associations_test.rb | 6 ++++++
 2 files changed, 10 insertions(+)

diff --git a/activerecord/lib/active_record/associations/belongs_to_association.rb b/activerecord/lib/active_record/associations/belongs_to_association.rb
index adb6af7165..58c9648ce8 100644
--- a/activerecord/lib/active_record/associations/belongs_to_association.rb
+++ b/activerecord/lib/active_record/associations/belongs_to_association.rb
@@ -20,6 +20,10 @@ module ActiveRecord
 
       private
 
+        def find_target?
+          !loaded? && foreign_key_present? && klass
+        end
+
         def update_counters(record)
           counter_cache_name = reflection.counter_cache_column
 
diff --git a/activerecord/test/cases/associations/belongs_to_associations_test.rb b/activerecord/test/cases/associations/belongs_to_associations_test.rb
index 818902beb5..866a3cca10 100644
--- a/activerecord/test/cases/associations/belongs_to_associations_test.rb
+++ b/activerecord/test/cases/associations/belongs_to_associations_test.rb
@@ -352,6 +352,12 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
     assert_equal members(:groucho), sponsor.sponsorable
   end
 
+  def test_dont_find_target_when_foreign_key_is_null
+    tagging = taggings(:thinking_general)
+    queries = assert_sql { tagging.super_tag }
+    assert_equal 0, queries.length
+  end
+
   def test_field_name_same_as_foreign_key
     computer = Computer.find(1)
     assert_not_nil computer.developer, ":foreign key == attribute didn't lock up" # '