We now have operators that support filtering for null/empty values in grid columns.  These are available using the standard Filter Menu, which provides input fields and the operator dropdown list.  Our users really love the Multi Checkbox filtering, which allows them to choose any number of possible values at the same time.  The missing feature is that the Multi Checkbox filtering prevents us from finding the "empty" rows.

Much the same way that "Select All" is automatically added to the list of checkboxes, please add some sort of "null/empty" item to the list.  It would be great if this was configurable.  In some of our columns, it's not possible to have empty values, so it doesn't make sense to include the "empty" checkbox for those columns.

Be sure to handle scenarios when the data source is automatic based on the data in the grid and when a separate, custom data source is provided for the column.