DateTimeField can now have the empty string as default value.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@12940 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5Form/FormulatorPatch.py

@@ -746,7 +746,10 @@ class PatchedDateTimeWidget(DateTimeWidget):
         if not hasattr(field, 'sub_form'):
             field.sub_form = create_datetime_text_sub_form()
 
-        if value is None and field.get_value('default_now'):
+        # Is it still usefull to test the None value,
+        # as DateTimeField should be considerer as the other field
+        # and get an empty string as default value?
+        if value in (None, '') and field.get_value('default_now'):
             value = DateTime()
         year   = None
         month  = None