ruby-on-rails-3 - 运行黄瓜时动作视图模板错误

Question

这是一个黄瓜场景：

Scenario: Login
Given the user is on Login page
When I sign in

我的步骤定义：

When /I sign in/ do
  within("#mypage") do
    fill_in 'login_id', :with => 'ccd'
    fill_in 'password', :with => 'coffee'
  end
  click_button 'Login'
  visit '/feedbacks/'
end

当我运行黄瓜时，我收到以下错误：

Scenario: Login                 # features\heartbeat_tests.feature:20
Given the user is on Login page # features/step_definitions/heartbeat_definitions.rb:5
When I sign in                  # features/step_definitions/heartbeat_definitions.rb:18
undefined method `each' for nil:NilClass (ActionView::Template::Error)
D:/shoutout_web/app/views/layouts/application.html.erb:256:in          
`_app_views_layouts_application_html_erb__124036717_28160832'