code: func (b *BufferedSeriesIterator) Next() bool {
  	if !b.ok {
  		return false
  	}
  
  	// Add current element to buffer before advancing.
  	b.buf.add(b.it.At())
  
  	b.ok = b.it.Next()
  	if b.ok {
  		b.lastTime, _ = b.Values()
  	}
  
  	return b.ok
  }
docs: // Next advances the iterator to the next element.