#vulnerable code 
                                void download(HttpClient httpClient, List<Asset> assets, Path relativePath) throws UncheckedIOException {
        Path outputFolder = folder.resolve(relativePath);

        keyBagManager.update(httpClient, assets);

        XFileKeyFactory fileKeys = new XFileKeyFactory(keyBagManager::keyBag);
        FileAssembler fileAssembler = new FileAssembler(fileKeys, outputFolder);

        AuthorizedAssets authorizedAssets = authorizeAssets.authorize(httpClient, assets);

        assetDownloader.accept(httpClient, authorizedAssets, fileAssembler);
    } 
                            #location 9 
                            #vulnerability type THREAD_SAFETY_VIOLATION
#fixed code
                                void download(HttpClient httpClient, List<Asset> assets, Path relativePath) {
        if (assets.isEmpty()) {
            return;
        }

        Path outputFolder = folder.resolve(relativePath);

        keyBagManager.update(httpClient, assets);

        XFileKeyFactory fileKeys = new XFileKeyFactory(keyBagManager::keyBag);
        FileAssembler fileAssembler = new FileAssembler(fileKeys, outputFolder);

        authorizeAssets.apply(httpClient, assets)
                .ifPresent(u -> assetDownloader.accept(httpClient, u, fileAssembler));

    }