#vulnerable code 
                                @Override
    protected File postDownload(File archive) {
        log.trace("PhatomJS package name: {}", archive);

        File extractFolder = archive.getParentFile().listFiles()[0];
        log.trace("PhatomJS extract folder (to be deleted): {}", extractFolder);

        File binFolder = new File(
                extractFolder.getAbsoluteFile() + separator + "bin");
        // Exception for older version of PhantomJS
        int binaryIndex = 0;
        if (!binFolder.exists()) {
            binFolder = extractFolder;
            binaryIndex = 3;
        }

        log.trace("PhatomJS bin folder: {} (index {})", binFolder, binaryIndex);

        File phantomjs = binFolder.listFiles()[binaryIndex];
        log.trace("PhatomJS binary: {}", phantomjs);

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

        downloader.renameFile(phantomjs, target);
        downloader.deleteFolder(extractFolder);
        return target;
    } 
                            #location 5 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Override
    protected File postDownload(File archive) {
        log.trace("PhatomJS package name: {}", archive);

        File extractFolder = archive.getParentFile()
                .listFiles(getFolderFilter())[0];
        log.trace("PhatomJS extract folder (to be deleted): {}", extractFolder);

        File binFolder = new File(
                extractFolder.getAbsoluteFile() + separator + "bin");
        // Exception for older version of PhantomJS
        int binaryIndex = 0;
        if (!binFolder.exists()) {
            binFolder = extractFolder;
            binaryIndex = 3;
        }

        log.trace("PhatomJS bin folder: {} (index {})", binFolder, binaryIndex);

        File phantomjs = binFolder.listFiles()[binaryIndex];
        log.trace("PhatomJS binary: {}", phantomjs);

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

        downloader.renameFile(phantomjs, target);
        downloader.deleteFolder(extractFolder);
        return target;
    }