code: public void write(Command cmd)
          throws IOException, IllegalArgumentException {
          //we delete the initial reply when the first command is sent
          if (cmd == null) {
              throw new IllegalArgumentException("null argument: cmd");
          }
          if (logger.isDebugEnabled()) {
              logger.debug("Control channel sending: " + cmd);
          }
          writeStr(cmd.toString());
      }
docs: Sends the command over the control channel.
  Do not wait for reply.
  @throws java.io.IOException on I/O error
  @param cmd FTP command