backbone update attributes return 204 instead of 422

gistfile1.coffee

#in my controller

  def update
  	user = current_user.update_attributes(params[:user])
  	respond_with user
  end

#in my backbone view

    @model.url = '/api/users'
    attributes = 
      name: $("#user_name").val()
      country: $("#user_country").val()
      timezone: $("#user_timezone").val()
      url: $("#user_url").val()
    @model.save attributes,
      wait: true
      success: =>
        show_notice("Profile Saved.")
        $(".profile_form").modal("hide")
        console.log "submit success"
        console.log @model
        upView = new Dnscell.Views.user_profile(model: @model)
        $(".content_inside").html(upView.render().el)
      error: @handleError