Sinatra-authentication has n, bug

gistfile1.rb

require 'sinatra'
require "digest/sha1"
require 'rack-flash'
require "dm-core"
#for using auto_migrate!
require "dm-migrations"
require "sinatra/reloader"
require 'haml'

require "sinatra-authentication"
use Rack::Session::Cookie, :secret => 'A1 sauce 1s  on a11 yr s'
#if you want flash messages
use Rack::Flash
DataMapper.setup( :default, "sqlite3://#{Dir.pwd}/test.db" )


class DmUser
#  include DataMapper::Resource
  property :name, String
#  property :id, Serial, :key => true
  has n, :things
end


class Thing
  include DataMapper::Resource
  property :name, String, :key => true
  belongs_to :dm_user
end

DataMapper.finalize
DataMapper.auto_migrate!
bob = DmUser.create(:name => "bob", :email => "[email protected]")
bob.save!
Thing.create(:name => "green thing", :dm_user_id => bob.id)

#this works
Thing.first.dm_user

#this does not
DmUser.first.things