How to use Excel based login script with Selenium webdriver?

I am completely new to selenium as well as Java coding and I am trying to execute excel based login script -- Selenium webdriver java. I am having 2 problems :

1. I am not able to iterate for loop to read all the records, only 1st row data is correctly processed and then gives nullpointerexception
2. And my password for all the account is 123456 but selenium is passing it as 123456.0 and I am getting error due to this.

If any one has better scripts which actually run that is also acceptable since I have searched many code but I am not able to run then.

Below is my code :

public class Excel_Read_Write {


    public static void main(String[] args)throws Exception  
    {


        // TODO Auto-generated method stub
         System.setProperty("webdriver.chrome.driver","C:\\chromedriver.exe");
         WebDriver driver = new ChromeDriver();
    // To Maximize browser screen       
//       FileInputStream fs = new FileInputStream("C:\\LoginDetails.xls");
//          driver.manage().window().maximize();    
            String baseUrl = "http://openspace.website/vpms/public/";
            driver.get(baseUrl);
            driver.manage().timeouts().implicitlyWait(10, TimeUnit.SECONDS);


//          String filePath = System.getProperty("user.dir")+"\\src\\excel_read_write";
            String filePath = System.getProperty("user.dir")+"\\src";
//          FileInputStream fs = new FileInputStream(filePath);

            String FilePath = "F:\\\\LoginDetails.xlsx";

            XSSFWorkbook wb = new XSSFWorkbook(FilePath);
            XSSFSheet s1 = wb.getSheetAt(0);
            int totalNoOfRows  = s1.getLastRowNum();
            int noOfColumns = s1.getRow(0).getPhysicalNumberOfCells();
            System.out.println(noOfColumns);
//          int totalNoOfCols = s1.getLastCellNum();
            System.out.println(noOfColumns);
            XSSFCell username,password;
             for(int i = 1; i < totalNoOfRows ; i++) {
                 for (int j=0; j < noOfColumns - 1; j++) {
                        username= s1.getRow(1).getCell(j);
                        password = s1.getRow(1).getCell(i);
                        System.out.println("Username"+username);
                        System.out.println("Password"+password);
                        driver.findElement(By.id("email")).clear();
                        driver.findElement(By.id("password")).clear();
                        driver.manage().timeouts().implicitlyWait(3, TimeUnit.SECONDS);
                        driver.findElement(By.id("email")).sendKeys(username.toString());
                        driver.findElement(By.id("password")).sendKeys(password.toString());
                        driver.findElement(By.xpath("/html/body/div/div/div[3]/section/form/div[3]/button")).click();
                        driver.manage().timeouts().implicitlyWait(10, TimeUnit.SECONDS);
                         if ((driver.getPageSource().contains("Check In"))){
                                System.out.println("Successful Login verified for " +username.toString());
                                driver.findElement(By.xpath("//*[@id=\"bs-example-navbar-collapse-1\"]/ul/li[4]/a")).click();
                                driver.manage().timeouts().implicitlyWait(10, TimeUnit.SECONDS);
                            } else {
                                System.out.println("Successful Login not verified for " +username.toString());
                            }
                 }
             }

Error message displayed :

Starting ChromeDriver 2.34.522940 (1a76f96f66e3ca7b8e57d503b4dd3bccfba87af1) on port 29074
Only local connections are allowed.
log4j:WARN No appenders could be found for logger (org.apache.http.client.protocol.RequestAddCookies).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
Jan 09, 2018 12:28:43 PM org.openqa.selenium.remote.ProtocolHandshake createSession
INFO: Detected dialect: OSS
3
3
UsernameQA Master
Password1.0
Successful Login not verified for QA Master
Username1.0
Password1.0
Successful Login not verified for 1.0
UsernameQA Master
Passwordnull
Exception in thread "main" java.lang.NullPointerException
    at excel_read_write.Excel_Read_Write.main(Excel_Read_Write.java:69)