#vulnerable code 
                                @Override
    public String downloadFromServer(RemoteUrl remoteUrl, String fileName, String localFileDir, String localFileDirTemp,
                                     String copy2TargetDirPath, boolean enableLocalDownloadDirInClassPath,
                                     int retryTimes, int retrySleepSeconds)
            throws Exception {

        // 目标地址文件
        File localFile = null;

        //
        // 进行下载、mv、copy
        //

        try {

            // 可重试的下载
            File tmpFilePathUniqueFile = retryDownload(localFileDirTemp, fileName, remoteUrl, retryTimes,
                    retrySleepSeconds);

            // 将 tmp file copy localFileDir
            localFile = transfer2SpecifyDir(tmpFilePathUniqueFile, localFileDir, fileName, false);

            // mv 到指定目录
            if (copy2TargetDirPath != null) {

                //
                if (enableLocalDownloadDirInClassPath || !copy2TargetDirPath.equals(ClassLoaderUtil.getClassPath
                        ())) {
                    localFile = transfer2SpecifyDir(tmpFilePathUniqueFile, copy2TargetDirPath, fileName, true);
                }
            }

            LOGGER.debug("Move to: " + localFile.getAbsolutePath());

        } catch (Exception e) {

            LOGGER.warn("download file failed, using previous download file.", e);
        }

        //
        // 判断是否下载失败
        //

        if (!localFile.exists()) {
            throw new Exception("target file cannot be found! " + fileName);
        }

        //
        // 下面为下载成功
        //

        // 返回相对路径
        if (localFileDir != null) {
            String relativePathString = OsUtil.getRelativePath(localFile, new File(localFileDir));
            if (relativePathString != null) {
                if (new File(relativePathString).isFile()) {
                    return relativePathString;
                }
            }
        }

        // 否则, 返回全路径
        return localFile.getAbsolutePath();
    } 
                            #location 44 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Override
    public String downloadFromServer(RemoteUrl remoteUrl, String fileName, String localFileDir, String localFileDirTemp,
                                     String copy2TargetDirPath, boolean enableLocalDownloadDirInClassPath,
                                     int retryTimes, int retrySleepSeconds)
            throws Exception {

        // 目标地址文件
        File localFile = null;

        //
        // 进行下载、mv、copy
        //

        try {

            // 可重试的下载
            File tmpFilePathUniqueFile = retryDownload(localFileDirTemp, fileName, remoteUrl, retryTimes,
                    retrySleepSeconds);

            // 将 tmp file copy localFileDir
            localFile = transfer2SpecifyDir(tmpFilePathUniqueFile, localFileDir, fileName, false);

            // mv 到指定目录
            if (copy2TargetDirPath != null) {

                //
                if (enableLocalDownloadDirInClassPath || !copy2TargetDirPath.equals(ClassLoaderUtil.getClassPath
                        ())) {
                    localFile = transfer2SpecifyDir(tmpFilePathUniqueFile, copy2TargetDirPath, fileName, true);
                }
            }

            LOGGER.debug("Move to: " + localFile.getAbsolutePath());

        } catch (Exception e) {

            LOGGER.warn("download file failed, using previous download file.", e);
        }

        //
        // 判断是否下载失败
        //
        
        if (localFile == null || !localFile.exists()) {
            throw new Exception("target file cannot be found! " + fileName);
        }

        //
        // 下面为下载成功
        //

        // 返回相对路径
        String relativePathString = OsUtil.getRelativePath(localFile, new File(localFileDir));
        if (relativePathString != null) {
            if (new File(relativePathString).isFile()) {
                return relativePathString;
            }
        }

        // 否则, 返回全路径
        return localFile.getAbsolutePath();
    }