Catch use case when language is an empty string.

bt5/erp5_base/SkinTemplateItem/portal_skins/erp5_base/NotificationTool_getDocumentValue.xml

@@ -65,7 +65,7 @@ portal_catalog = portal.portal_catalog\n
 valid_portal_type_list = (\'Notification Message\',)\n
 \n
 # Find the applicable language\n
-if language is None:\n
+if language in (None, \'\'):\n
   language = portal.Localizer.get_selected_language()\n
 \n
 # Find the default language\n

bt5/erp5_base/bt/revision

-987
\ No newline at end of file
+988
\ No newline at end of file