How to Pass Blank/Empty Date to Webbi prompt?

Hello,

I have a query in webbi and I want it to have two prompts:

1) show dates > the date entered, easy enough.

2) Also show all records that do not have a date populated. How do I pass a blank/empty date via the date prompt in webbi?

Source is a BEx query. These parameters will be filled and report launched from an opendoc URL via Dashboards.

Thank you!