FilterExpression And The SQLDataSource Control

I have a SQLDatasource control on a web page. It is the datasource for a gridview control.

I want the gridview to show all jones if the FirstName textbox is left blank or empty. Right now I have to put a % in the FirstName textbox to get what I want.
If I make the FirstNameTextBox empty or remove the % from the FirstNameTextbox it returns all the names in the database no matter what the last name is.

How do I get it to work without having to use the % in the FirstName Textbox? THANKS!


FilterExpression="LastName LIKE '%{0}%' and FirstName LIKE '%{1}%'">
<FilterParameters>
            <asp:ControlParameter ControlID="LastNameTextBox" Name="LastName" PropertyName="Text" DefaultValue="" />
            <asp:ControlParameter ControlID="FirstNameTextBox" Name="FirstName" PropertyName="Text" DefaultValue="" />
</FilterParameters>

Last Name: Jones___________
First Name: %_____________
FILTERBUTTON

Gridview
Last Name      First Name
Bob                Jones
Bill                 Jones