问为什么我要为这个NoMethodError打devise_group电话？

EN

class ApplicationController < ActionController::Base
  # Prevent CSRF attacks by raising an exception.
  protect_from_forgery with: :exception

  devise_group :user, contains: [:manager, :employee]
end

source 'https://rubygems.org'
ruby '2.2.2'
gem 'rails', '4.2.3'
gem 'sqlite3'
gem 'sass-rails', '~> 5.0'
gem 'uglifier', '>= 1.3.0'
gem 'coffee-rails', '~> 4.1.0'
gem 'jquery-rails'
gem 'turbolinks'
gem 'jbuilder', '~> 2.0'
gem 'foundation-rails'
gem 'simple_form'
gem 'devise'
group :development do
  gem 'better_errors'
  gem 'quiet_assets'
  gem 'rails_layout'
  gem 'spring-commands-rspec'
end
group :development, :test do
  gem 'factory_girl_rails'
  gem 'faker'
  gem 'rspec-rails'
  gem 'byebug'
  gem 'web-console', '~> 2.0'
  gem 'spring'
end
group :test do
  gem 'capybara'
  gem 'database_cleaner'
  gem 'launchy'
  gem 'selenium-webdriver'
end

class Manager < User
end

class Employee < User
end