Overrode Hash#nested_under_indifferent_access in HashWithIndifferentAccess

to return self.

activesupport/lib/active_support/hash_with_indifferent_access.rb

@@ -16,6 +16,10 @@ module ActiveSupport
       dup
     end
 
+    def nested_under_indifferent_access
+      self
+    end
+
     def initialize(constructor = {})
       if constructor.is_a?(Hash)
         super()

activesupport/test/core_ext/hash_ext_test.rb

@@ -121,6 +121,9 @@ class HashExtTest < Test::Unit::TestCase
 
     foo = { "foo" => NonIndifferentHash.new.tap { |h| h["bar"] = "baz" } }.with_indifferent_access
     assert_kind_of NonIndifferentHash, foo["foo"]
+
+    foo = { "foo" => IndifferentHash.new.tap { |h| h["bar"] = "baz" } }.with_indifferent_access
+    assert_kind_of IndifferentHash, foo["foo"]
   end
 
   def test_indifferent_assorted