请检查代码建议更正：
组件框架;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.time.Duration;
import org.apache.poi.ss.usermodel.Sheet;
import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.ss.usermodel.Workbook;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;
import org.apache.poi.hssf.usermodel.*;
import org.openqa.selenium.By;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.firefox.FirefoxDriver;

public class DataDriveFramework {
    public void readExcel(String filePath, String fileName, String sheetName) throws IOException {
        File file = new File(filePath+"\\"+fileName);
        FileInputStream fis = new FileInputStream(file);
        Workbook loginWorkbook=null;
        
        String fileExtension=fileName.substring(fileName.indexOf("."));
        if(fileExtension.equals(".xlsx"))
        {
            loginWorkbook=new XSSFWorkbook(fis);
        }
        else if(fileExtension.equals("xls"))
        {
            loginWorkbook=new HSSFWorkbook(fis);
    }
        Sheet loginSheet=loginWorkbook.getSheet(sheetName);
        
        int rowCount=loginSheet.getLastRowNum()-loginSheet.getFirstRowNum();
        for(int i=1;1<rowCount+1;i++)
        {
            Row row=loginSheet.getRow(i);
            String username=row.getCell(0).getStringCellValue();
            String password=row.getCell(0).getStringCellValue();
            test(username,password);
        }
}
    public void test(String username, String password)
    {
        WebDriver driver=new FirefoxDriver();
        driver.manage().timeouts().implicitlyWait(Duration.ofSeconds(10));
        
        String baseURL="https://accounts.google.com";
        driver.get(baseURL);
        
        driver.findElement(By.id("identifierId")).sendKeys(username);
        driver.findElement(By.xpath("/html/body/div[1]/div[1]/div[2]/div/c-wiz/div/div[2]/div/div[2]/div/div[1]/div/div/button/span")).click();
                
        driver.findElement(By.xpath("//*[@id=\"password\"]/div[1]/div/div[1]/input")).sendKeys(password);
        driver.findElement(By.xpath("//*[@id=\"passwordNext\"]/div/button/span")).click();
        driver.quit();
    }
    public static void main(String[] args)throws IOException {
        DataDriveFramework readFile=new DataDriveFramework();
        String filePath="C:\\Users\\Shefali\\eclipse-workspace\\DataDriveFramework\\TestExcelSheet\\";
        readFile.readExcel(filePath, "DataDriven.xls", "Sheet1");
    }
    
}

代码是从excel工作表中获取数据并自动登录。但我得到一个错误--

"Exception in thread "main" java.lang.NullPointerException: Cannot invoke "org.apache.poi.ss.usermodel.Workbook.getSheet(String)" because "loginWorkbook" is "null"
    at com.framework.DataDriveFramework.readExcel(DataDriveFramework.java:31)
    at com.framework.DataDriveFrame.main(DataDriveFrame.java:60)"