我是自動化領域的新手。這是我的簡單 TestNG 登錄代碼，當我以 TestNG 身份運行該代碼時，它會出現 java.lang.NullPointerException，雙擊它會突出顯示我導航到 URL 的位置。這是我的代碼。enter code herepackage Day5pkg;import java.util.concurrent.TimeUnit;import org.openqa.selenium.By;import org.openqa.selenium.WebDriver;import org.openqa.selenium.firefox.FirefoxDriver;import org.openqa.selenium.firefox.FirefoxDriver;import org.openqa.selenium.firefox.FirefoxOptions;import org.testng.annotations.AfterMethod;import org.testng.annotations.BeforeTest;import org.testng.annotations.Test;public class Day5 {    public WebDriver driver;@BeforeTest      public void beforeTest() {          System.setProperty("webdriver.firefox.driver","C:\\Users\\Nabila\\Downloads\\geckodriver-v0.26.0-win64\\geckodriver.exe");          FirefoxOptions options = new FirefoxOptions();            driver.navigate().to("http://www.demo.guru99.com/V4/");            driver.manage().timeouts().implicitlyWait(300, TimeUnit.SECONDS);            options.addArguments("test-type");            options.addArguments("start-maximized");            options.addArguments("--js-flags=--expose-gc");              options.addArguments("--enable-precise-memory-info");             options.addArguments("--disable-popup-blocking");            options.addArguments("--disable-default-apps");            options.addArguments("test-type=browser");            options.addArguments("disable-infobars");      }  @Test  (priority = 0)    public void login(){      driver = new FirefoxDriver();         driver.findElement(By.name("uid")).sendKeys("mngr231");         driver.findElement(By.name("password")).click();         driver.findElement(By.name("password")).sendKeys("ehyjusu");         driver.findElement(By.name("btnLogin")).click();            System.out.println("Manger Id : mngr230");      }