Delete Media URL from Stock Items

Hello,

I am trying to create an import scenario to delete the Media URL’s form a number of Stock Items.

I have tried =null, and blank entry imports, but am missing something.  It seems I need a delete Action, but there is none available in the import scenario for media urls.

Attached is the Import Scenario i’ve been using.  There’s a bunch of stuff on there, but I just need the Media URL’s for this.

Thanks!

Nathan