gistfile1.rb

#rails/actionpack/lib/action_view/helpers/form_helper.rb:508
if @object_name.sub!(/\[\]$/,'') 
  if object ||= @template_object.instance_variable_get("@#{Regexp.last_match.pre_match}") and object.respond_to?(:to_param) 
    @auto_index = object.to_param 
  else 
    raise ArgumentError, "object[] naming but object param and @object var don't exist or don't respond to to_param: #{object.inspect}" 
 end 
end