Add a test case for layout nil.

actionpack/lib/abstract_controller/layouts.rb

@@ -249,6 +249,7 @@ def conditional_layout?
       # Symbol:: call the method specified by the symbol, which will return the template name
       # false::  There is no layout
       # true::   raise an ArgumentError
+      # nil::    Force default layout behavior with inheritance
       #
       # ==== Parameters
       # * <tt>layout</tt> - The layout to use.

actionpack/test/abstract/layouts_test.rb

@@ -14,7 +14,10 @@ class Base < AbstractController::Base
         "layouts/overwrite.erb"         => "Overwrite <%= yield %>",
         "layouts/with_false_layout.erb" => "False Layout <%= yield %>",
         "abstract_controller_tests/layouts/with_string_implied_child.erb" =>
-                                           "With Implied <%= yield %>"
+                                           "With Implied <%= yield %>",
+        "abstract_controller_tests/layouts/with_grand_child_of_implied.erb" =>
+                                           "With Grand Child <%= yield %>"
+
       )]
     end
 
@@ -64,6 +67,10 @@ class WithStringImpliedChild < WithString
     class WithChildOfImplied < WithStringImpliedChild
     end
 
+    class WithGrandChildOfImplied < WithStringImpliedChild
+      layout nil
+    end
+
     class WithProc < Base
       layout proc { |c| "overwrite" }
 
@@ -299,6 +306,13 @@ class TestBase < ActiveSupport::TestCase
           assert_equal "With Implied Hello string!", controller.response_body
       end
 
+      test "when a grandchild has nil layout specified, the child has an implied layout, and the " \
+        "parent has specified a layout, use the child controller layout" do
+          controller = WithGrandChildOfImplied.new
+          controller.process(:index)
+          assert_equal "With Grand Child Hello string!", controller.response_body
+      end
+
       test "raises an exception when specifying layout true" do
         assert_raises ArgumentError do
           Object.class_eval do