InputStream和OutputStream抛出空指针异常？

Question

尝试将现有文件复制到新位置时，我的代码似乎抛出了空指针异常；新文件也将根据当前执行日期命名。

有什么想法吗？

public static String returnScreenshotName() {
    return (System.getProperty("user.dir") + "\\target\\output\\imgs\\" + screenshotName);
}

private static void copyFileUsingStream(File source, File dest) throws IOException {
    InputStream is = null;
    OutputStream os = null;
    try {
        is = new FileInputStream(source);
        os = new FileOutputStream(dest);
        byte[] buffer = new byte[1024];
        int length;
        while ((length = is.read(buffer)) > 0) {
            os.write(buffer, 0, length);
        }
    } catch (IOException ignored) {
    }
    finally {
        is.close();
        os.close();
    }
}

public static void copyLatestExtentReport() throws IOException {
    try {
        Date d = new Date();
        String date = d.toString().replace(":", "_").replace(" ", "_");
        File source = new File (System.getProperty("user.dir") + "\\output\\report1.html");
        File dest = new File (System.getProperty("user.dir") + "\\output\\" + date + ".html");
        copyFileUsingStream(source, dest);
    }catch (IOException ignored) {
    }