code: public function rpop(int $timeout = -1)
      {
          if ($timeout >= 0) {
              $ret = $this->redis->brpop($this->key, $timeout)[$this->key];
          } else {
              $ret = $this->redis->rpop($this->key);
          }
  
          return $this->unSerialize($ret);
      }
docs: @param int $timeout   Maximal time in seconds to wait for items to pop. Zero blocks until something becomes
  available.
  -1 to disable blocking and immediately return null if nothing is available to pop.
  
  @return mixed The removed item from the end of the list.
  Null in case the key does not contain a list or the timeout was
  triggered.