Index: django/contrib/admin/templatetags/admin_list.py
===================================================================
--- django/contrib/admin/templatetags/admin_list.py	(revision 11012)
+++ django/contrib/admin/templatetags/admin_list.py	(working copy)
@@ -208,7 +208,10 @@
             elif f.flatchoices:
                 result_repr = dict(f.flatchoices).get(field_val, EMPTY_CHANGELIST_VALUE)
             else:
-                result_repr = escape(field_val)
+                if field_val is not None:
+                    result_repr = escape(field_val)
+                else:
+                    result_repr = EMPTY_CHANGELIST_VALUE
         if force_unicode(result_repr) == '':
             result_repr = mark_safe(' ')
         # If list_display_links not defined, add the link tag to the first field