Add guard around course.email

Author: professor

app/views/courses/show.html.erb

@@ -26,10 +26,12 @@
   <tr class="cmu_table_odd">
     <td>Email:</td>
     <td>
-      <%= @course.email %>
-      <% if @course.updating_email %> (...updating...)
-      <% else %>
-          <%= link_to '(Who is on it?) ', mailing_list_path(@course.email) %>
+      <% if @course.email.present? %>
+          <%= @course.email %>
+          <% if @course.updating_email %> (...updating...)
+          <% else %>
+              <%= link_to '(Who is on it?) ', mailing_list_path(@course.email) %>
+          <% end %>
       <% end %>
     </td>
   </tr>