Merge pull request #4353 from dmathieu/hide_nil_unchecked_checkbox

don't set the hidden checkbox value if it's nil

actionpack/lib/action_view/helpers/form_helper.rb

@@ -1091,7 +1091,7 @@ def to_check_box_tag(options = {}, checked_value = "1", unchecked_value = "0")
         else
           add_default_name_and_id(options)
         end
-        hidden = tag("input", "name" => options["name"], "type" => "hidden", "value" => unchecked_value, "disabled" => options["disabled"])
+        hidden = unchecked_value ? tag("input", "name" => options["name"], "type" => "hidden", "value" => unchecked_value, "disabled" => options["disabled"]) : ""
         checkbox = tag("input", options)
         hidden + checkbox
       end

actionpack/test/template/form_helper_test.rb

@@ -374,6 +374,14 @@ def test_check_box_with_explicit_checked_and_unchecked_values
     )
   end
 
+  def test_check_box_with_nil_unchecked_value
+    @post.secret = "on"
+    assert_dom_equal(
+      '<input checked="checked" id="post_secret" name="post[secret]" type="checkbox" value="on" />',
+      check_box("post", "secret", {}, "on", nil)
+    )
+  end
+
   def test_check_box_with_multiple_behavior
     @post.comment_ids = [2,3]
     assert_dom_equal(