protected function getPropertyValidators(core_kernel_classes_Property $property)
    {
        $validators = parent::getPropertyValidators($property);

        $notEmptyProperties = [
            GenerisRdf::PROPERTY_USER_UILG,
            GenerisRdf::PROPERTY_USER_ROLES,
            OntologyRdfs::RDFS_LABEL,
        ];

        if ($this->isNew()) {
            $notEmptyProperties[] = GenerisRdf::PROPERTY_USER_PASSWORD;
            $notEmptyProperties[] = 'http://www.tao.lu/Ontologies/generis.rdf#login';
        }

        if (in_array($property->getUri(), $notEmptyProperties)) {
            $validators[] = 'notEmpty';
        }

        return $validators;
    }