Hidden Fields Picklist in Form - how to choose default value?

I’d like to ask the community for help.

I have a form where confirmation emails are sent based on a picklist. This allows me to send different email versions depending on the contact’s country. The deciding field is a <hiddenfield>“Country”.

Challenge:
I’d like Eloqua to send the confirmation email in English to contacts for whom the <hiddenfield> “Country” was not populated.

How should I configure the form’s Processing Steps so that, by default, the English version of the email is sent if the hidden field is not filled during the submission process?