Using RailsAdmin without devise

rails_admin_without_devise.rb

# add RailsAdmin to the Gemfile
# do NOT add devise
gem "rails_admin", :git => "git://github.com/sferik/rails_admin.git"

# run Bundler
bundle

# run the generator for RailsAdmin
# looks like it's broken, but it just does not install devise
# you may also remove the app/config/locales/devise.en.yml
rails generate rails_admin:install_admin
# create the history entity
rake db:migrate

# create an initializer for using CanCan with RailsAdmin
# found here: http://everydayrails.com/2010/12/17/rails-admin-panel.html
# config/initializers/rails_admin.rb
require "rails_admin/application_controller"

module RailsAdmin
  class ApplicationController < ::ApplicationController
    before_filter :can_admin?
    
    private
    
    def can_admin?
      raise CanCan::AccessDenied if current_user.nil? || !current_user.admin?
    end
  end

module RailsAdmin
  class ApplicationController < ::ApplicationController
    before_filter :can_admin?

    private

    def can_admin?
      raise CanCan::AccessDenied if current_user.nil? || !current_user.admin?
    end
  end

  # latest commits introduced new dependencies to devise...
  DEFAULT_CURRENT_USER = Proc.new do
    #return nil unless resource = Devise::mappings.keys.first {|r| signed_in?(r)}
    send("current_user")
  end

end

# RailsAdmin needs two additional things to get it working with my OmniAuth setup
# 1. an email attribute on the User class, which i simply redirected to the nickname
# app/models/user.rb
def email
  nickname
end

# 2. a logout route that matches Devises name schema
# config/routes.rb
match '/auth/destroy_user_session', :to => 'sessions#destroy_user_session', :as => :destroy_user_session

# this simply redirects to the original logout
# app/controllers/sessions_controller.rb
def destroy_user_session
  redirect_to destroy_session_path
end

I'm getting the following error:
ActionView::Template::Error (Could not find a valid mapping for #<User id
From here
6: - if _current_user
7: - if user_link = edit_user_link
8: %li= user_link
9: - if logout_path.present?
10: %li= link_to content_tag('span', t('admin.misc.log_out'), :class => 'label label-important'), logout_path, :method => Devise.sign_out_via
11: - if _current_user.respond_to?(:email) && _current_user.email.present?
12: %li= image_tag "#{(request.ssl? ? 'https://secure' : 'http://www')}.gravatar.com/avatar/#{Digest::MD5.hexdigest _current_user.email}?s=30", :style => 'padding-top:5px'
devise (2.2.3) lib/devise/mapping.rb:42:in find_scope!' /home/eugene/.bundler/ruby/1.9.1/rails_admin-75079da0906e/app/helpers/rails_admin/application_helper.rb:36:inlogout_path'

Any help would be appreciated!

me too ,I don't want to use devise ,and do as rails_admin wiki help .define my own authticate function .but still have this error . why?