how to return blank values with checked checkbox

How to return blank values from datagridview columns using checkbox, who is checked. So how it is in both pictures, I want to filter blank rows without date and it should work as filter as blank.

That checkbox gets data from database.

I tried some if statements in my sql procedure.

if @INNOT_CLOSED_CARDS is not null
        set @WHERE = @WHERE + 'AND EXISTS (select hosp_ID from D3_HOSPITALIZATION
            where isnull(CLOSE_DATE,'''') = '''')'

Or something like this.

if @INNOT_CLOSED_CARDS = 1
    BEGIN
        set @WHERE = @WHERE + ' AND (CLOSE_DATE is null)'
    END ELSE if @INNOT_CLOSED_CARDS = 0
    BEGIN
        set @WHERE = @WHERE + ' AND (CLOSE_DATE is not null)'
    END

Well, it does nothing.