static invalid(reason, explanation = null) {
    if (!reason) {
      throw new InvalidArgumentError("need to specify a reason the Duration is invalid");
    }

    const invalid = reason instanceof Invalid ? reason : new Invalid(reason, explanation);

    if (Settings.throwOnInvalid) {
      throw new InvalidDurationError(invalid);
    } else {
      return new Duration({ invalid });
    }
  }
Create an invalid Duration.
@param {string} reason - simple string of why this datetime is invalid. Should not contain parameters or anything else data-dependent
@param {string} [explanation=null] - longer explanation, may include parameters and other useful debugging information
@return {Duration}