code: func (b *Base64) SetBSON(raw bson.Raw) error {
  	var m bson.M
  	if err := raw.Unmarshal(&m); err != nil {
  		return err
  	}
  
  	if data, ok := m["data"].(string); ok {
  		*b = Base64(data)
  		return nil
  	}
  
  	return errors.New("couldn't unmarshal bson raw value as Base64")
  }
docs: // SetBSON sets the Base64 from raw bson data