message: checkStopTransaction - minor change
diff: @@ -428,7 +428,7 @@ export default abstract class BillingIntegration<T extends BillingSetting> {
  });
  }
  // Check Charging Station
  - if (transaction.billingData.invoiceID) {
  + if (transaction?.billingData.invoiceID) {
  throw new BackendError({
  message: 'Transaction has already billing data',
  source: Constants.CENTRAL_SERVER,
  