code: public synchronized Transaction getIncompleteRefundTransaction() {
          checkState(refundTx != null);
          if (stateMachine.getState() == State.INITIATED) {
              stateMachine.transition(State.WAITING_FOR_SIGNED_REFUND);
          }
          return refundTx;
      }
docs: Returns a partially signed (invalid) refund transaction that should be passed to the server. Once the server
  has checked it out and provided its own signature, call
  {@link PaymentChannelV1ClientState#provideRefundSignature(byte[], KeyParameter)} with the result.