NoMethodError in Frontend#course

Showing /var/www/clients/client1/web1/web/www/app/apps/themes/launch_de/views/template_course.html.erb where line #61 raised:

undefined method `name' for nil:NilClass
Extracted source (around line #61):
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</div>
<div class="room"><strong><%= t('views.frontend.courses.room') %>:</strong> <%= @course.course_room.name %></div>
<div class="categories">

Rails.root: /var/www/clients/client1/web1/web/www

Application Trace | Framework Trace | Full Trace

Request

Parameters:

{"category_id"=>"_gup4439a425k3903k4787k8614ke2a5923f6b1f",
 "start"=>"2015-01-05",
 "slug"=>"langhantel-kursraum-1-mon-17-30-18-20-0"}

Response

Headers:

None