diff --git a/tabellio/documents/common.py b/tabellio/documents/common.py
index b36c63c..ac72a34 100644
--- a/tabellio/documents/common.py
+++ b/tabellio/documents/common.py
@@ -7,7 +7,10 @@ import tabellio.config.utils
 class BasePublication(object):
     @property
     def date_str(self):
-        return self.date.strftime('%d/%m/%Y')
+        try:
+            return self.date.strftime('%d/%m/%Y')
+        except AttributeError:
+            return ''
 
     def get_authors_as_string(self):
         if not self.authors: