Clearance不显示闪烁消息(Ruby on Rails 5.0.1)

class ApplicationController < ActionController::Base
  before_action :set_flash_messages

  private

  def set_flash_messages
    flash.discard(:notice) if flash[:notice].blank?
    flash.discard(:alert) if flash[:alert].blank?
  end
end

<% if flash[:notice].present? %>
  <div class="alert alert-success">
    <%= flash[:notice] %>
  </div>
<% end %>

<% if flash[:alert].present? %>
  <div class="alert alert-danger">
    <%= flash[:alert] %>
  </div>
<% end %>

Clearance.configure do |config|
  # 其他配置...

  config.middleware.use Clearance::Middleware, raise_on_unauthorized: false do |env|
    request = Rack::Request.new(env)
    if Clearance.configuration.allow_sign_in_without_confirmation?
      env['clearance.flash'] = nil
    end
  end
end

Rails.application.routes.draw do
  resources :sessions, only: [:new, :create, :destroy] do
    get 'success', on: :collection, to: 'sessions#success'
  end
end

class SessionsController < ApplicationController
  def success
    flash[:notice] = 'You have successfully signed in.'
    redirect_to root_url
  end
end