code: func (c *Controller) addToBin(ntfr *notifier, address []byte) (symKeyId string, pssAddress pss.PssAddress, err error) {
  
  	// parse the address from the message and truncate if longer than our bins threshold
  	if len(address) > ntfr.threshold {
  		address = address[:ntfr.threshold]
  	}
  
  	pssAddress = pss.PssAddress(address)
  	hexAddress := fmt.Sprintf("%x", address)
  	currentBin, ok := ntfr.bins[hexAddress]
  	if ok {
  		currentBin.count++
  		symKeyId = currentBin.symKeyId
  	} else {
  		symKeyId, err = c.pss.GenerateSymmetricKey(ntfr.topic, pssAddress, false)
  		if err != nil {
  			return "", nil, err
  		}
  		ntfr.bins[hexAddress] = &sendBin{
  			address:  address,
  			symKeyId: symKeyId,
  			count:    1,
  		}
  	}
  	return symKeyId, pssAddress, nil
  }
docs: // check if we already have the bin
  // if we do, retrieve the symkey from it and increment the count
  // if we dont make a new symkey and a new bin entry