code: private void notifyOnValidationFailure(@NonNull final Validator<ValueType> validator) {
          for (ValidationListener<ValueType> listener : listeners) {
              listener.onValidationFailure(this, validator);
          }
      }
docs: Notifies all registered listeners, that a validation failed.
  
  @param validator
  The validator, which failed, as an instance of the type {@link Validator}. The
  validator may not be null