clearing session variables

[mojodojo]

I have some forms that I have in a wizard type of layout. You get a couple of fields to fill out and then you can click a next or back button and those buttons post the values into session variables. Now here is my question. The way I have it set now, is that if you set the session variable you can't set it to Null. Here is an example of my code.

if ($GET[CaseNumber]){
$SESSION[CaseNumber] = $_GET[CaseNumber];
}

Now, how would I set the value to nothing? I could use a space to clear text boxes, but that doesn't work for checkboxes or radios.

Thanks

[rheroux]

$_SESSION['CaseNumber'] = "" will set it to nothing while preserving the variable still.