Filtering DataViews

Question

Thanks for tour post 

Filter data dispalyed in a DataGridView using BindingSource and DataView

I have a question:

 

I have DataView with a column in Date format and I want to have two filters:

 

1 - by empty dates .

 

2- by not empty dates

 

How can I express the criteria string?

 

Forgive me for my poor english.