Cannt能够在硒中找到元素

Question

我的编码找不到元素。请任何人帮助我摆脱我的错误。

测试用例

    @Test 
public void main() throws Exception {
    Thread.sleep(5000);
    System.out.println("Before sign in action execution");
    SignIn_Action.Execute(iTestCaseRow);
}

SignIn_Action

    public class SignIn_Action{
       public static void Execute(int iTestCaseRow) throws Exception{
           // Fetch user name from Excel
           String sUserName = ExcelUtils.getCellData(iTestCaseRow, Constant.col_UserName);
           System.out.println("User Name read from --> "+ sUserName);
           // Fetch password from Excel
           String sPassword = ExcelUtils.getCellData(iTestCaseRow, Constant.col_Password);
           System.out.println("Password read from excel --> "+ sPassword);
           LoginPageObjects.txtbx_username().sendKeys(sUserName);
           LoginPageObjects.txtbx_password().sendKeys(sPassword);
           LoginPageObjects.btn_login().click();
   }

LoginPageObject类

    public class LoginPageObjects extends BaseClass {
    private static WebElement element = null; 
    public LoginPageObjects(WebDriver driver){
        super(driver);
    }

     public static WebElement txtbx_username(){  
        try {       
        WebElement element = null;          
        System.out.println("Inside txtbx_username method");      
        element = driver.findElement(By.name("first_name"));        
        System.out.println("Fetched element name is : "+element);    
        Log.info("Username text box found");
        }catch (Exception e){        
            Log.error("UserName text box is not found on the Login Page");
            throw(e);
            } 
        return element;
        }
}
}

BaseClass的

    public class BaseClass {
    public static WebDriver driver;
    public static boolean bResult;
    public  BaseClass(WebDriver driver){
        BaseClass.driver = driver;
        BaseClass.bResult = true;
    }
}

我的问题在以下代码中

element = driver.findElement(By.name("first_name"));

此代码不是find元素，它显示在下面的错误消息

java.lang.NullPointerException
at pageObjects.LoginPageObjects.txtbx_username(LoginPageObjects.java:27)