protected function _getListFieldsNullVal() {
		$result = [];
		$schema = $this->schema();
		$data = array_filter(
			$schema,
			function ($v, $k) {

				return isset($v['null']) && $v['null'] === true;
			},
			ARRAY_FILTER_USE_BOTH
		);
		if (!empty($data)) {
			$result = array_keys($data);
		}

		return $result;
	}