Add another default-value for tardiness

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

@@ -104,7 +104,7 @@
       <td style="color: {{ absence_reason.colour }};">
         {{ participation.absence_reason.short_name }}
       </td>
-      <td>{{ participation.tardiness }}</td>
+      <td>{{ participation.tardiness|default_if_none:"" }}</td>
     </tr>
   {% endfor %}
   </tbody>