Return nil from read_attribute(:foo) if 'foo' is not present in the @…

…attributes hash, but the _foo method has been defined. This brings the behaviour into line with the 3-0-stable branch and the master branch before 93641ed (there were previously no assertions about this which is why the change slipped through). Note that actually calling the 'foo' method will still raise an error if the attribute is not present.

activerecord/lib/active_record/attribute_methods/read.rb

@@ -100,7 +100,7 @@ def _#{method_name}
       # "2004-12-12" in a data column is cast to a date object, like Date.new(2004, 12, 12)).
       def read_attribute(attr_name)
         if respond_to? "_#{attr_name}"
-          send "_#{attr_name}"
+          send "_#{attr_name}" if @attributes.has_key?(attr_name.to_s)
         else
           _read_attribute attr_name
         end

activerecord/test/cases/finder_test.rb

@@ -247,9 +247,10 @@ def test_unexisting_record_exception_handling
   def test_find_only_some_columns
     topic = Topic.find(1, :select => "author_name")
     assert_raise(ActiveModel::MissingAttributeError) {topic.title}
+    assert_nil topic.read_attribute("title")
     assert_equal "David", topic.author_name
     assert !topic.attribute_present?("title")
-    #assert !topic.respond_to?("title")
+    assert !topic.attribute_present?(:title)
     assert topic.attribute_present?("author_name")
     assert_respond_to topic, "author_name"
   end