addError(key, error) {
    if (error instanceof SetOptionError) {
      const { errors } = error;
      for (const optionKey of Object.keys(errors)) {
        this.addError(optionKey, errors[optionKey]);
      }

      return;
    }

    this.errors[key] = error;
    this.message = combinePathErrors(this);
  }
add message
@param {String} key
@param {String|Error} error
@api private