code: public static Validator blankOr(Validator validator) {
      Preconditions.checkNotNull(validator, "validator cannot be null.");
      return BlankOrValidator.of(validator);
    }
docs: Method will return a validator that will accept a blank string. Any other value will be passed on to the supplied validator.
  
  @param validator Validator to test non blank values with.
  @return validator that will accept a blank string. Any other value will be passed on to the supplied validator.