Ensure lines exist in the basket before accessing them.

ecommerce/extensions/basket/tests/test_views.py

@@ -769,12 +769,14 @@ class VoucherAddViewTests(LmsApiMockMixin, TestCase):
 
     def test_no_voucher_error_msg(self):
         """ Verify correct error message is returned when voucher can't be found. """
+        self.basket.add_product(ProductFactory())
         self.assert_form_valid_message("Coupon code '{code}' does not exist.".format(code=COUPON_CODE))
 
     def test_voucher_already_in_basket_error_msg(self):
         """ Verify correct error message is returned when voucher already in basket. """
-        voucher = factories.VoucherFactory(code=COUPON_CODE)
+        voucher, product = prepare_voucher(code=COUPON_CODE)
         self.basket.vouchers.add(voucher)
+        self.basket.add_product(product)
         self.assert_form_valid_message(
             "You have already added coupon code '{code}' to your basket.".format(code=COUPON_CODE))
 

ecommerce/extensions/basket/views.py

@@ -464,7 +464,7 @@ class VoucherAddView(BaseVoucherAddView):  # pylint: disable=function-redefined
 
     def form_valid(self, form):
         code = form.cleaned_data['code']
-        if not self.request.basket.id:
+        if self.request.basket.is_empty:
             return redirect_to_referrer(self.request, 'basket:summary')
         if self.request.basket.contains_voucher(code):
             messages.error(