#vulnerable code 
                                @Override
    protected File postDownload(File archive) {
        log.trace("Post processing for Opera: {}", archive);

        File extractFolder = archive.getParentFile()
                .listFiles(getFolderFilter())[0];
        if (!extractFolder.isFile()) {
            log.trace("Opera extract folder (to be deleted): {}",
                    extractFolder);
            File operadriver = extractFolder.listFiles()[0];
            log.trace("Operadriver binary: {}", operadriver);

            File target = new File(archive.getParentFile().getAbsolutePath(),
                    operadriver.getName());
            log.trace("Operadriver target: {}", target);

            downloader.renameFile(operadriver, target);
            downloader.deleteFolder(extractFolder);
            return target;
        } else {
            return super.postDownload(archive);
        }
    } 
                            #location 10 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Override
    protected File postDownload(File archive) {
        log.trace("Post processing for Opera: {}", archive);

        File extractFolder = archive.getParentFile()
                .listFiles(getFolderFilter())[0];
        if (!extractFolder.isFile()) {
            log.trace("Opera extract folder (to be deleted): {}",
                    extractFolder);
            File[] listFiles = extractFolder.listFiles();
            int i = 0;
            File operadriver;
            do {
                operadriver = listFiles[0];
                i++;
            } while (!config().isExecutable(operadriver)
                    || i >= listFiles.length);

            log.trace("Operadriver binary: {}", operadriver);

            File target = new File(archive.getParentFile().getAbsolutePath(),
                    operadriver.getName());
            log.trace("Operadriver target: {}", target);

            downloader.renameFile(operadriver, target);
            downloader.deleteFolder(extractFolder);
            return target;
        } else {
            return super.postDownload(archive);
        }
    }