docs: private void setCommandHeader(CommandType command) {
          String header;
          if (command instanceof ConnectCommand) {
              header = FtpMessage.OPEN_COMMAND;
          } else if (command instanceof GetCommand) {
              header = FTPCmd.RETR.getCommand();
          } else if (command instanceof PutCommand) {
              header = FTPCmd.STOR.getCommand();
          } else if (command instanceof ListCommand) {
              header = FTPCmd.LIST.getCommand();
          } else if (command instanceof DeleteCommand) {
              header = FTPCmd.DELE.getCommand();
          } else {
              header = command.getSignal();
          }
  
          setHeader(FtpMessageHeaders.FTP_COMMAND, header);
      }