code: func (s *IndicesFlushService) WaitIfOngoing(waitIfOngoing bool) *IndicesFlushService {
  	s.waitIfOngoing = &waitIfOngoing
  	return s
  }
docs: // WaitIfOngoing, if set to true, indicates that the flush operation will
  // block until the flush can be executed if another flush operation is
  // already executing. The default is false and will cause an exception
  // to be thrown on the shard level if another flush operation is already running..