code: func fixupTxnOp(rawOp interface{}) error {
  	rawMap, ok := rawOp.(map[string]interface{})
  	if !ok {
  		return fmt.Errorf("unexpected raw op type: %T", rawOp)
  	}
  	for k, v := range rawMap {
  		switch strings.ToLower(k) {
  		case "kv":
  			if v == nil {
  				return nil
  			}
  			return decodeValue(v)
  		}
  	}
  	return nil
  }
docs: // fixupTxnOp looks for non-nil Txn operations and passes them on for
  // value conversion.