code: func (h *BytesRefHash) Clear(resetPool bool) {
  	h.lastCount = h.count
  	h.count = 0
  	if resetPool {
  		h.pool.Reset(false, false) // we don't need to 0-fill the bufferes
  	}
  	h.bytesStart = h.bytesStartArray.Clear()
  	if h.lastCount != -1 && h.shrink(h.lastCount) {
  		// shurnk clears the hash entries
  		return
  	}
  	for i, _ := range h.ids {
  		h.ids[i] = -1
  	}
  }
docs: /* Clears the BytesRef which maps to the given BytesRef */