value of checbkox/radio defaults to "on" when not specified

lib/capybara/node/simple.rb

@@ -82,6 +82,8 @@ module Capybara
             option = native.xpath(".//option[@selected='selected']").first || native.xpath(".//option").first
             option[:value] || option.content if option
           end
+        elsif tag_name == 'input' && %w(radio checkbox).include?(native[:type])
+          native[:value] || 'on'
         else
           native[:value]
         end

lib/capybara/rack_test/form.rb

@@ -28,7 +28,10 @@ class Capybara::RackTest::Form < Capybara::RackTest::Node
       case field.name
       when 'input'
         if %w(radio checkbox).include? field['type']
-          merge_param!(params, field['name'].to_s, field['value'].to_s) if field['checked']
+          if field['checked']
+            node=Capybara::RackTest::Node.new(self.driver, field)
+            merge_param!(params, field['name'].to_s, node.value.to_s)
+          end          
         elsif %w(submit image).include? field['type']
           # TO DO identify the click button here (in document order, rather
           # than leaving until the end of the params)

lib/capybara/spec/session/node_spec.rb

@@ -67,6 +67,16 @@ Capybara::SpecHelper.spec "node" do
       @session.find('//textarea[1]').set("some <em>html</em> here")
       @session.find('//textarea[1]').value.should == "some <em>html</em> here"
     end
+    
+    it "defaults to 'on' for checkbox" do
+      @session.visit('/form')
+      @session.find('//input[@id="valueless_checkbox"]').value.should == 'on'
+    end
+
+    it "defaults to 'on' for radio buttons" do
+      @session.visit('/form')
+      @session.find('//input[@id="valueless_radio"]').value.should == 'on'
+    end    
   end
 
   describe "#set" do