java.lang.NullPointerException for TestNG classes

Null point exception occurring because of driver instance you are initiating begin differently than later.
Please create and use driver instance as a global variable 

static WebDriver driver;
-------------------------------------------------------------------------------------------
OR

Singleton is solution for null point exception in your test automation 

Create class and by using method you can use driver instance any where without any issue like null point 

import org.openqa.selenium.By;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.chrome.ChromeDriver;
import org.openqa.selenium.chrome.ChromeOptions;
import org.openqa.selenium.support.ui.ExpectedConditions;
import org.openqa.selenium.support.ui.WebDriverWait;

import java.io.File;
import java.net.URISyntaxException;
import java.net.URL;
import java.nio.file.Paths;

public class TestApp {
    private WebDriver driver;
    private static TestApp myObj;
    // public static WebDriver driver;
    utils.PropertyFileReader property = new PropertyFileReader();

    public static TestApp getInstance() {
        if (myObj == null) {
            myObj = new TestApp();
            return myObj;
        } else {
            return myObj;
        }
    }

    //get the selenium driver
    public WebDriver getDriver()
    {
        return driver;
    }

    //when selenium opens the browsers it will automatically set the web driver
    private void setDriver(WebDriver driver) {
        this.driver = driver;
    }

    public static void setMyObj(TestApp myObj) {
        TestApp.myObj = myObj;
    }

    public void openBrowser() {


        //String chromeDriverPath = property.getProperty("config", "chrome.driver.path");
        //String chromeDriverPath = property.getProperty("config", getChromeDriverFilePath());
        System.setProperty("webdriver.chrome.driver", getChromeDriverFilePath());
        ChromeOptions options = new ChromeOptions();
        options.addArguments("--disable-notifications");
        options.addArguments("disable-infobars");
        driver = new ChromeDriver(options);
        driver.manage().window().maximize();
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }



    public void navigateToURL() {

        String url =property.getProperty("config","url");
     ;
        driver.get(url);
    }

    public void closeBrowser()
    {
        driver.quit();
    }

    public WebElement waitForElement(By locator, int timeout)
    {
        WebElement element = new WebDriverWait(TestApp.getInstance().getDriver(), timeout).until
                (ExpectedConditions.presenceOfElementLocated(locator));
        return element;
    }

    private String getChromeDriverFilePath()
    {
        // checking resources file for chrome driver in side main resources
        URL res = getClass().getClassLoader().getResource("chromedriver.exe");
        File file = null;
        try {
            file = Paths.get(res.toURI()).toFile();
        } catch (URISyntaxException e) {
            e.printStackTrace();
        }
        return file.getAbsolutePath();
    }
}


//If you want call driver instance you can use following line 

**TestApp.getInstance().getDriver();**