fix error when news have not end publication datetime p/tango#240

newsbox/models.py

@@ -307,7 +307,7 @@ class NewsboxExpiredBase(six.with_metaclass(NewsboxModelBase, models.Model)):
     def publish(self, commit=True):
         updated = super(NewsboxExpiredBase, self).publish(commit=False)
         now_datetime = now()
-        if now_datetime > self.newsbox_publication_end_date:
+        if self.newsbox_publication_end_date and now_datetime > self.newsbox_publication_end_date:
             self.newsbox_publication_end_date = None
             updated = True
         if updated and commit: