refactor grouped_options_for_select

actionpack/lib/action_view/helpers/form_options_helper.rb

@@ -472,16 +472,16 @@ def option_groups_from_collection_for_select(collection, group_method, group_lab
       # <b>Note:</b> Only the <tt><optgroup></tt> and <tt><option></tt> tags are returned, so you still have to
       # wrap the output in an appropriate <tt><select></tt> tag.
       def grouped_options_for_select(grouped_options, selected_key = nil, prompt = nil)
-        body = ''
-        body << content_tag(:option, prompt, { :value => "" }, true) if prompt
+        body = "".html_safe
+        body.safe_concat content_tag(:option, prompt, :value => "") if prompt
 
         grouped_options = grouped_options.sort if grouped_options.is_a?(Hash)
 
-        grouped_options.each do |group|
-          body << content_tag(:optgroup, options_for_select(group[1], selected_key), :label => group[0])
+        grouped_options.each do |label, container|
+          body.safe_concat content_tag(:optgroup, options_for_select(container, selected_key), :label => label)
         end
 
-        body.html_safe
+        body
       end
 
       # Returns a string of option tags for pretty much any time zone in the