Use empty string, not None, for ShippingAddress fields
Use empty string, not None, for ShippingAddress fields

As per
https://github.com/django-oscar/django-oscar-paypal/commit/9db799178124c11ae370a9c6bea73e27b643dde2,
shipping address fields are never allowed to be None.

hastexo/django-oscar-vat_moss,fghaas/django-oscar-vat_moss,arbrandes/django-oscar-vat_moss,fghaas/django-oscar-vat_moss,hastexo/django-oscar-vat_moss,arbrandes/django-oscar-vat_moss