Automatically grab billing address if shipping address is empty

Hi there,

I think I’m trying to do something relatively simple, but I just can’t seem to figure it out. I’m using woocommerce and a plugin to export all my orders to my shipment partner. But my customers are not obliged to give a different shipping address (they can use their billing address and use a checkbox if they want a different shipping address). So I would like the billing address to automatically (this doesn’t have to be visible for the customer) filled in if the shipping address is left empty, this way I can export the shipping address for sending purposes. Is there a simple plugin? Or some code to add somewhere?

Thanks!
Rosalie