空指针异常即将到来

Question

public static WebDriver getscreenshot(String path) throws Exception 
{
    WebDriver driver = null;
    TakesScreenshot ts = (TakesScreenshot)driver;
    File scrFile = ts.getScreenshotAs(OutputType.FILE);
    FileUtils.copyFile(scrFile, new File(path));
    return driver;
}

我得到了上述代码的空指针异常。