FX.php, AddDBParam

I am trying to do a search and display records that have a certain field empty. Here is my code, when I search, I get the error code that says no records match.

$DataQuery->AddDBParam('assignDate', '', 'eq');

As you can see I am looking at assignDate and checking to see if it is equal to nothing. Any help would be greatly appreciated. I have only 1 record that is ID=1, receiveDate=5/14/2004, assignDate=, resolveDate=

So it should work?

<?php

include_once($HTTP_SERVER_VARS['DOCUMENT_ROOT'] . "/FX/FX.php");

include_once($HTTP_SERVER_VARS['DOCUMENT_ROOT'] . "/FX/server_data.php");

$DataQuery = new FX($serverIP, $webCompanionPort);

$DataQuery->SetDBData("webtest.fp5");

$DataQuery->AddDBParam('assignDate', '', 'eq');

$DataResults = $DataQuery-> FMFind();

print_r($DataResults);

?>