#vulnerable code 
                                public synchronized void download(URL url, String version, String export,
            List<String> driverName) throws IOException {
        File targetFile = new File(getTarget(version, url));
        File binary = null;

        // Check if binary exists
        boolean download = !targetFile.getParentFile().exists()
                || (targetFile.getParentFile().exists()
                        && targetFile.getParentFile().list().length == 0)
                || override;

        if (!download) {
            // Check if existing binary is valid
            Collection<File> listFiles = FileUtils
                    .listFiles(targetFile.getParentFile(), null, true);
            for (File file : listFiles) {
                for (String s : driverName) {
                    if (file.getName().startsWith(s) && file.canExecute()) {
                        binary = file;
                        log.debug(
                                "Using binary driver previously downloaded {}",
                                binary);
                        download = false;
                        break;
                    } else {
                        download = true;
                    }
                }
                if (!download) {
                    break;
                }
            }
        }

        if (download) {
            File temporaryFile = new File(targetFile.getParentFile(), UUID.randomUUID().toString());
            log.info("Downloading {} to {}", url, temporaryFile);
            WdmHttpClient.Get get = new WdmHttpClient.Get(url)
                    .addHeader("User-Agent", "Mozilla/5.0")
                    .addHeader("Connection", "keep-alive");

            try {
                FileUtils.copyInputStreamToFile(
                    httpClient.execute(get).getContent(), temporaryFile);
            }
            catch (IOException e) {
                temporaryFile.delete();
                throw e;
            }

            log.info("Renaming {} to {}", temporaryFile, targetFile);
            temporaryFile.renameTo(targetFile);

            if (!export.contains("edge")) {
                binary = extract(targetFile, export);
            } else {
                binary = targetFile;
            }

            if (targetFile.getName().toLowerCase().endsWith(".msi")) {
                binary = extractMsi(targetFile);
            }

        }
        if (export != null) {
            browserManager.exportDriver(export, binary.toString());
        }
    } 
                            #location 66 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                public synchronized void download(URL url, String version, String export,
            List<String> driverName) throws IOException {
        File targetFile = new File(getTarget(version, url));
        File binary = null;

        // Check if binary exists
        boolean download = !targetFile.getParentFile().exists()
                || (targetFile.getParentFile().exists()
                        && targetFile.getParentFile().list().length == 0)
                || override;

        if (download) {
            File temporaryFile = new File(targetFile.getParentFile(),
                    randomUUID().toString());
            log.info("Downloading {} to {}", url, temporaryFile);
            WdmHttpClient.Get get = new WdmHttpClient.Get(url)
                    .addHeader("User-Agent", "Mozilla/5.0")
                    .addHeader("Connection", "keep-alive");

            try {
                copyInputStreamToFile(httpClient.execute(get).getContent(),
                        temporaryFile);
            } catch (IOException e) {
                temporaryFile.delete();
                throw e;
            }

            log.info("Renaming {} to {}", temporaryFile, targetFile);
            temporaryFile.renameTo(targetFile);

            if (!export.contains("edge")) {
                binary = extract(targetFile, export);
            } else {
                binary = targetFile;
            }

            if (targetFile.getName().toLowerCase().endsWith(".msi")) {
                binary = extractMsi(targetFile);
            }

        } else {
            // Check if existing binary is valid
            Collection<File> listFiles = listFiles(targetFile.getParentFile(),
                    null, true);
            for (File file : listFiles) {
                for (String s : driverName) {
                    if (file.getName().startsWith(s) && file.canExecute()) {
                        binary = file;
                        log.debug(
                                "Using binary driver previously downloaded {}",
                                binary);
                        download = false;
                        break;
                    } else {
                        download = true;
                    }
                }
                if (!download) {
                    break;
                }
            }
        }

        if (export != null && binary != null) {
            browserManager.exportDriver(export, binary.toString());
        }
    }