Error: System.NullReferenceException error in Selenium with NUnit

Question

I'm getting following error at verification stage:

"An unhandled exception of type 'System.NullReferenceException' occurred in nunit.framework.dll

Additional information: Object reference not set to an instance of an object."

code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using NUnit.Framework;
using OpenQA.Selenium;
using OpenQA.Selenium.Firefox;
using OpenQA.Selenium.Support.UI;
using System.Globalization;
using System.Threading.Tasks;

namespace Login_Val_Test_Do_Not_Use
{
    class Program
    {
        static void Main(string[] args)
        {

            //Instantiate Firefox Driver
            //Go to CV Library Website
            var driver = new FirefoxDriver();
            driver.Navigate().GoToUrl("https://www.cv-library.co.uk/");

            //Wait for web element to become visible
            System.Threading.Thread.Sleep(15000);

            //Click on Login button
            driver.FindElement(By.XPath(".//*[@id='home-nav-right']/a[1]")).Click();

            //Verification that specified page opens
            var loggedInHeader = driver.FindElement(By.Id("cand-login-tabs"));
            Assert.IsTrue(loggedInHeader.Displayed, "Unable to access page");

            }
    }
}

Answer 1

If you're getting the error on the assertion line, it's exactly what the message tells you - you're getting a null reference. Often this is due to the fact that your FindElement() fails, so then when you try to access one of the methods or properties (e.g. click() or Displayed), you get a null reference error since the object isn't what you think it is (it's null because the element wasn't found).

For debugging, you can just add some checks after each of the FindElement() calls to verify an element was found, but really, the stack trace/console logging should point you to the exact line that failed.

Answer 2

The following should work. I've used the class name for the login button instead of using XPath (seems more appropriate here) + always use explicit waits never Thread.sleep!

//Instantiate Firefox Driver
//Go to CV Library Website
var driver = new FirefoxDriver();
driver.Navigate().GoToUrl("https://www.cv-library.co.uk/");

WebDriverWait wait = new WebDriverWait(driver, TimeSpan.FromSeconds(15));
IWebElement loginButton = wait.Until(ExpectedConditions.ElementToBeClickable(By.ClassName("nav-login")));

loginButton.Click();

//Verification that specified page opens
var loggedInHeader = wait.Until(ExpectedConditions.ElementIsVisible(By.Id("cand-login-tabs")));
Assert.IsTrue(loggedInHeader.Displayed, "Unable to access page");