采用screenshotSession ID为空时出现异常。在调用quit()后使用WebDriver？(TestNG)

import org.testng.ITestResult;
import org.testng.annotations.AfterMethod;
import org.testng.annotations.Test;

public class MyTest {
    private WebDriver driver;

    @Test
    public void myTest() {
        // 测试逻辑代码
        // ...
    }

    @AfterMethod
    public void afterMethod(ITestResult result) {
        if (result.getStatus() == ITestResult.FAILURE) {
            // 截图操作
            TakesScreenshot screenshot = (TakesScreenshot) driver;
            File srcFile = screenshot.getScreenshotAs(OutputType.FILE);
            // 保存截图文件
            // ...
        }
        // 关闭浏览器会话
        driver.quit();
    }
}