public function onConfigImporterValidate(ConfigImporterEvent $event) {
$importer = $event
->getConfigImporter();
$importList = $importer
->getStorageComparer()
->getSourceStorage()
->listAll();
if (empty($importerList)) {
throw new ConfigImporterException("This import will delete all your active configuration, I'm bailing out now.");
}
}