code: func (n *node) KeyExists(bucketName string, key interface{}) (bool, error) {
  	id, err := toBytes(key, n.codec)
  	if err != nil {
  		return false, err
  	}
  
  	var exists bool
  	return exists, n.readTx(func(tx *bolt.Tx) error {
  		bucket := n.GetBucket(tx, bucketName)
  		if bucket == nil {
  			return ErrNotFound
  		}
  
  		v := bucket.Get(id)
  		if v != nil {
  			exists = true
  		}
  
  		return nil
  	})
  }
docs: // KeyExists reports the presence of a key in a bucket.