Resolve "Add export functionality to course book"

Closes #258 (closed)

aleksis/apps/alsijil/templates/alsijil/partials/person_overview.html

@@ -61,7 +61,7 @@
       {% endfor %}
       <tr>
         <th colspan="3">{% trans 'Tardiness' %}</th>
-        <td>{{ person.tardiness_sum }}'/{{ person.tardiness_count }}&times;</td>
+        <td>{{ person.tardiness_sum|default_if_none:0 }}'/{{ person.tardiness_count }}&times;</td>
       </tr>
     </table>
   </div>