docs: public void purchaseReservedEipInMonth(String eip, int reservationLength) {
          Billing billing = new Billing();
          billing.setReservation(new Billing.Reservation().withReservationLength(reservationLength));
          this.purchaseReservedEip(new PurchaseReservedEipRequest().withEip(eip).withBilling(billing));
      }