docs: public String command(String command, boolean sync)
      {
          Utils.checkArgument(
                              !CONFIG.equals(command),
                              "CONFIG is not useable with that API. Please use configure(ZMsg) method");
          Utils.checkArgument(
                              !RESTART.equals(command),
                              "RESTART is not useable with that API. Please use restart(ZMsg) method");
          if (STATUS.equals(command)) {
              return status(sync);
          }
          if (EXIT.equals(command)) {
              return exit();
          }
          // consume the status in the pipe
          String status = recvStatus();
  
          if (agent.send(command)) {
              // the pipe is refilled
              if (sync) {
                  status = status(true);
              }
          }
          return status;
      }