public function buildKeysChoices(MediaImport $import)
    {
        $prefix = $import->getFilesystem();
        $fs = $this->mountManager->getFilesystem($prefix);
        $contents = $fs->listContents('', true);
        $choices = [];
        foreach ($contents as $object) {
            if (!($object['type'] == 'dir' || substr($object['path'], 0, 1) == '.')) {
                $key = sprintf('%s://%s', $prefix, $object['path']);
                $choices[$key] = $object['path'];
            }
        }
        return $choices;
    }