How make Rabl works with ActionController::Metal

I’ve took this post like basis but receive empty response every time. What’s wrong?

Basic controller:

class Api::V1::BaseController < ActionController::Metal
  include AbstractController::Rendering
  include AbstractController::Callbacks
  include AbstractController::Helpers

  include ActionController::HttpAuthentication::Token::ControllerMethods
  include ActionController::Rendering
  include ActionController::Renderers::All
  include ActionController::MimeResponds
  include ActionController::Instrumentation

  append_view_path "#{Rails.root}/app/views"

  respond_to :
json
end

Controller:

class Api::V1::UsersController < Api::V1::BaseController

  def index
@user = User.find(params[:id])
  end

end

RABL template:

object @user

attributes :first_name