Filter SP2010 List View

I've tried searching for this, but maybe I'm using the wrong terms - I can't find what I'm looking for.

I have a product list with expiry dates, but not all products have an expiry date.  I want to look at a view of the list where the expiry date is not empty, I assume I do this with a filter, but I can't workout how to filter on a 'value exists' or 'does-not-exist' basis.

Current settings (filter via web interface:
When column: Expiry Date
contains
*

Note that the column value IS a date, which might complicate things further.

I also want to be able to use this filter in SPD2010 so that a workflow that checks expiry date against current date will stop if there is no expiry date set.

Thanks in advance.