'shipaddresslist' value empty on PO

We have identified a bug with purchase orders (we drop ship all orders) where the 'shipaddresslist' field (i.e. the ship address internal id) is null/empty on some PO's. When this value is empty on PO's, we cannot pull the shipping address via script and we can't save changes to the PO without selecting a value in that field. We have created a workaround but the workaround is costly in script processing time.

As I mentioned, we drop ship all orders. When a SO is approved, a drop ship PO is automatically created by NS. When this PO is created, we use an after submit user event script to send the PO information to our vendor. Part of the info we have to send is the customer's shipping address. When the 'shipaddresslist' value is empty on the PO, we cannot pull the address from the PO record. In the script, we have to load the SO and get the address from there which is adds to processing time.