Make url_for work when option is nil and default_url_options has

stringified keys

actionpack/lib/action_dispatch/routing/url_for.rb

@@ -145,7 +145,7 @@ module ActionDispatch
       def url_for(options = nil)
         case options
         when nil
-          _routes.url_for(url_options)
+          _routes.url_for(url_options.symbolize_keys)
         when Hash
           symbolized = {}
           options.keys.each do |k|

actionpack/test/controller/url_for_test.rb

@@ -365,6 +365,15 @@ module AbstractController
         assert_equal("/c/a", W.new.url_for(:controller => 'c', :action => 'a', :only_path => true))
       end
 
+      def test_with_stringified_default_url_options_and_without_options
+        W.default_url_options['controller'] = 'c'
+        W.default_url_options['only_path']  = true
+        assert_equal("/c", W.new.url_for)
+
+        W.default_url_options['action'] = 'a'
+        assert_equal("/c/a", W.new.url_for)
+      end
+
       def test_url_params_with_nil_to_param_are_not_in_url
         assert_equal("/c/a", W.new.url_for(:only_path => true, :controller => 'c', :action => 'a', :id => Struct.new(:to_param).new(nil)))
       end