Kevin,
I just tried this out in Mendix 10.17.0 with the most recent Datagrid 2 version installed. Setting the Default Filter to empty worked in this scenario. Are you using an older version of DataWidgets module? If so, maybe upgrading would help.
Mike
To filter a Data Grid 2 to show only objects with no date set by default, follow these steps:
If the grid still displays all objects, double-check that the filter is correctly configured and that there are no conflicting settings or conditions in the grid’s properties.