Handle the (unexpected, by me at least) case where there is

no revision_date - display   instead of "None"
 - Legacy-Id: 867

Author: fenner

ietf/templates/idindex/doclist.html

@@ -18,7 +18,7 @@
 <tr bgcolor="{% cycle #efefff,#dfdfff %}">
 {# use url here! #}
 <td><a href="/drafts/{{ draft.filename }}/">{{ draft.filename }}-{{ draft.revision_display }}</a></td>
-<td>{{ draft.revision_date }}</td>
+<td>{% firstof draft.revision_date &nbsp; %}</td>
 <td>{{ draft.status }}</td>
 {% if norfc %}
 {% else %}