code: func (tab *Table) nodeToRevalidate() (n *node, bi int) {
  	tab.mutex.Lock()
  	defer tab.mutex.Unlock()
  
  	for _, bi = range tab.rand.Perm(len(tab.buckets)) {
  		b := tab.buckets[bi]
  		if len(b.entries) > 0 {
  			last := b.entries[len(b.entries)-1]
  			return last, bi
  		}
  	}
  	return nil, 0
  }
docs: // nodeToRevalidate returns the last node in a random, non-empty bucket.