multiple filters expressions for SqlDataSource

[ZBoT]

Hi! I am trying to filter a SqlDataSource based on two fields
(textboxes). They both don't have to be filled out at the same time
although they can be. Currently when I run if I do not fill out one of
the textboxes it does not filter at all. If I fill them both out it
filters properly. Anyone know how to correct this? Any help is MUCH
appreciated. Thanks!

FilterExpression="name='{0}' and job_num='{1}'">
<FilterParameters>
<asp:ControlParameter Name="name" ControlId="nameTextbox"
PropertyName="Text"/>
<asp:ControlParameter Name="job_num" ControlId="jobTextBox"
PropertyName="Text"/>
</FilterParameters>