code: @Override
      public Optional<Transport> getTransportParam() throws SipParseException {
          try {
              final Optional<Buffer> transport = getParameter(SipParser.TRANSPORT);
              return transport.map(Transport::of);
          } catch (final IllegalArgumentException e) {
              throw new SipParseException(0, e.getMessage(), e);
          }
      }
docs: /*
  @Override
  public void setPort(final int port) {
  this.isDirty = true;
  if (port < 0) {
  this.port = null;
  } else {
  this.port = Buffers.wrap(port);
  }
  }