测试方法“” System.NullReferenceException：未将对象引用设置为对象的实例

Question

我收到此异常：

测试方法 OnlineBankingTests.ConnectNativeSmokeTest.CNLoginTests.VerifyLoginNoBlankPwd 抛出异常： System.NullReferenceException：未将对象引用设置为对象的实例。 堆栈跟踪： CNLoginPage.PasswordRequired() 第 577 行 CNLoginTests.VerifyLoginNoBlankPwd() 第 78 行

但是，对我来说，对象似乎被引用了......我有点迷茫。

    [TestMethod]
    [TestCategory("CNSmoke")]
    public void VerifyLoginNoBlankPwd()
    {
        CanRun();

        // Arrange
        var baseUrl = Settings.ConnectNativeURL;

        var loginPage = new CNLoginPage(ConnectNativeDriver); // Isnt it creating a reference here to the class that contains the PasswordRequired() method??

        // Verify Password is Required
        loginPage.GoTo(baseUrl);
        loginPage.PasswordRequired(); // Line 78
        Assert.IsTrue(
            loginPage.IsBlankPasswordErrorSuccessful(),
            "Leaving Password blank didn't produce expected error.");
    }

---

public class CNLoginPage
{

    public void PasswordRequired()
    {
        var userId = _driver.GetElementByCssSelector("#username");
        userId.SendKeys("TESTER"); // Line 577

        var password = _driver.GetElementByCssSelector("#password");
        password.SendKeys(" ");

        var enter = _driver.GetElementByCssSelector("#AutomatedTesting-loginButton");
        enter.Click();
    }

}