Similar update... the value would be:
<?php echo((isset($_GET["invalid"])?ValidatedField("allshows2update","deadline"):"".(($row_WADAallshows2["deadline"] && date('n/d/Y',strtotime($row_WADAallshows2['deadline'])) != "11/30/-0001")?date("n/d/Y",strtotime($row_WADAallshows2["deadline"])):"")."")); ?>
To update the database, just go to the database table design and check the checkbox for "allow null" and save your changes