update cart

pkg/voucher/service.go

@@ -71,6 +71,14 @@ func (sf *StateFile) GetVoucher(code string) (*Voucher, bool) {
 func LoadStateFile(fileName string) (*StateFile, error) {
 	f, err := os.Open(fileName)
 	if err != nil {
+		if os.IsNotExist(err) {
+			return &StateFile{
+				State: State{
+					Vouchers: []Voucher{},
+				},
+				Version: 1,
+			}, nil
+		}
 		return nil, err
 	}
 	defer f.Close()