title: Solution to NullPointerException in my TestNG test case
body: <p>I am trying to login Facebook by using multiple sets of login cridential from external excel sheet using <code>TestNG</code> but in between the code what i have written throws:</p>
  
  <pre><code>FAILED: f
  java.lang.NullPointerException
      at DataDriven.loginRetesting.f(loginRetesting.java:31)
      at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
      at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
      at java.lang.reflect.Method.invoke(Method.java:601)
      at org.testng.internal.MethodInvocationHelper.invokeMethod(MethodInvocationHelper.java:84)
      at org.testng.internal.Invoker.invokeMethod(Invoker.java:714)
      at org.testng.internal.Invoker.invokeTestMethod(Invoker.java:901)
      at org.testng.internal.Invoker.invokeTestMethods(Invoker.java:1231)
      at org.testng.internal.TestMethodWorker.invokeTestMethods(TestMethodWorker.java:127)
      at org.testng.internal.TestMethodWorker.run(TestMethodWorker.java:111)
      at org.testng.TestRunner.privateRun(TestRunner.java:767)
      at org.testng.TestRunner.run(TestRunner.java:617)
      at org.testng.SuiteRunner.runTest(SuiteRunner.java:334)
      at org.testng.SuiteRunner.runSequentially(SuiteRunner.java:329)
      at org.testng.SuiteRunner.privateRun(SuiteRunner.java:291)
      at org.testng.SuiteRunner.run(SuiteRunner.java:240)
      at org.testng.SuiteRunnerWorker.runSuite(SuiteRunnerWorker.java:52)
      at org.testng.SuiteRunnerWorker.run(SuiteRunnerWorker.java:86)
      at org.testng.TestNG.runSuitesSequentially(TestNG.java:1224)
      at org.testng.TestNG.runSuitesLocally(TestNG.java:1149)
      at org.testng.TestNG.run(TestNG.java:1057)
      at org.testng.remote.RemoteTestNG.run(RemoteTestNG.java:111)
      at org.testng.remote.RemoteTestNG.initAndRun(RemoteTestNG.java:204)
      at org.testng.remote.RemoteTestNG.main(RemoteTestNG.java:175)
  </code></pre>
  
  <p>Code:</p>
  
  <pre><code>@Test
    public void f() throws Exception{
        FileInputStream fi=new FileInputStream("E:\\workspace99\\SeleniumAutomations\\testdata\\LoginData.xls");
        Workbook w=Workbook.getWorkbook(fi);
        Sheet s=w.getSheet(0);
        for (int i = 1; i &lt; 8; i++) {
            driver.findElement(By.id("email")).sendKeys(s.getCell(0,i).getContents());
            driver.findElement(By.id("pass")).sendKeys(s.getCell(1,i).getContents());
            driver.findElement(By.id("u_0_1")).click();
            Thread.sleep(1000);
            if (selenium.isElementPresent("id=userNavigationLabel")) {
                //driver.findElement(By.cssSelector("span.gb_V.gbii")).click();
                driver.findElement(By.id("userNavigationLabel")).click();
                driver.findElement(By.cssSelector("input.uiLinkButtonInput")).click();
                Thread.sleep(1000);
            }
                else{
                    System.out.println("invalid cridential");
                    driver.findElement(By.id("email")).clear();
                    driver.findElement(By.id("pass")).clear();
  
                }
  
  
          }
  
      }
  </code></pre>
  
  <p>I am not able to find out where the problem is? so how to solve it. </p>