class ActionView::Helpers::Tags::CollectionCheckBoxes

def hidden_field
  hidden_name = @html_options[:name]
  hidden_name ||= if @options.has_key?(:index)
    "#{tag_name_with_index(@options[:index])}[]"
  else
    "#{tag_name}[]"
  end
  @template_object.hidden_field_tag(hidden_name, "", id: nil)
end

def render(&block)
  rendered_collection = render_collection do |item, value, text, default_html_options|
    default_html_options[:multiple] = true
    builder = instantiate_builder(CheckBoxBuilder, item, value, text, default_html_options)
    if block_given?
      @template_object.capture(builder, &block)
    else
      render_component(builder)
    end
  end
  # Append a hidden field to make sure something will be sent back to the
  # server if all check boxes are unchecked.
  rendered_collection + hidden_field
end

def render_component(builder)
  builder.check_box + builder.label
end