a

You have a nil object when you didn't expect it!
You might have expected an instance of Array.
The error occurred while evaluating nil.each
Extracted source (around line #44):

41: 
42: 
43: <ol class="noDots">
44:   <% @screenings.each do |screening| %>
45:    <li> 
46:      <h3><%= screening.cinema.name %></h3>
47:    </li>

html.erb

<ol class="noDots">
  <% @screenings.each do |screening| %>
   <li> 
     <h3><%= screening.cinema.name %></h3>
   </li>
  <% end %>
</ol>