Updated Drupal to 8.6. This goes with the following updates because it's possible...

[yaffs-website] / web / core / lib / Drupal / Core / Config / UnsupportedDataTypeConfigException.php

<?php

namespace Drupal\Core\Config;

/**
 * Exception thrown when a config data type is invalid.
 */
class UnsupportedDataTypeConfigException extends ConfigException {
}