paperwork: Hide list addresses in department cert view if None

paperwork/templates/paperwork/department_certifications.dj.html

@@ -16,7 +16,7 @@
           <tr>
             <td>{{ department.name }}</td>
             <td>{{ department.shop_lead_flag.members.all|join:", " }}</td>
-            <td><a href="mailto:{{ department.list_address }}">{{ department.list_address }}</a></td>
+            <td>{% if department.list_address is not none %}<a href="mailto:{{ department.list_address }}">{{ department.list_address }}</a>{% endif %}</td>
           </tr>
         {% endfor %}
       </tbody>