code: public function execute(Command $command)
      {
          $response = $this->getActiveNode()->execute($command, $this->api);
  
          // if more than 1 node configured, lets try a different node up to max connection attempts
          if (empty($response) && count($this->nodes) > 1 && $this->attempts < $this->getConfigValue('max_connect_attempts')) {
              $response = $this->pickNewNode()->execute($command);
          } elseif (empty($response) && $this->attempts >= $this->getConfigValue('max_connect_attempts')) {
              throw new Exception('Nodes unreachable. Error Msg: ' . $this->api->getError());
          } elseif ($response == false) {
              throw new Exception('Command failed to execute against Riak. Error Msg: ' . $this->api->getError());
          }
  
          return $response;
      }
docs: Execute a Riak command
  
  @param Command $command
  @return Command\Response
  @throws Exception