code: private Validator<ValueType> validateLeft() {
          Validator<ValueType> result = null;
          Collection<Validator<ValueType>> subValidators = onGetLeftErrorMessage();
  
          if (subValidators != null) {
              for (Validator<ValueType> validator : subValidators) {
                  notifyOnValidationFailure(validator);
  
                  if (result == null) {
                      result = validator;
                  }
              }
          }
  
          for (Validator<ValueType> validator : validators) {
              if (!validator.validate(getValue())) {
                  notifyOnValidationFailure(validator);
  
                  if (result == null) {
                      result = validator;
                  }
              }
          }
  
          return result;
      }
docs: Validates the current value of the view in order to retrieve the error message and icon,
  which should be shown at the left edge of the view, if a validation fails.
  
  @return The validator, which failed or null, if the validation succeeded