code: func (c *Client) putLabel(ctx context.Context, tx *bolt.Tx, l *platform.Label) error {
  	v, err := json.Marshal(l)
  	if err != nil {
  		return &platform.Error{
  			Err: err,
  		}
  	}
  
  	key, pe := labelKey(l)
  	if pe != nil {
  		return pe
  	}
  
  	if err := tx.Bucket(labelBucket).Put(key, v); err != nil {
  		return &platform.Error{
  			Err: err,
  		}
  	}
  
  	return nil
  }
docs: // set a label and overwrite any existing label