While using TestNg framework my code throwing NullPointerException

Question

I want to use TestNg in my learning project. While using TestNg framework, i am getting NullPointer Excetion. I think problem is in WebDriver object declaration part. But i don't know how i can implement the same. Can any one help me on the same?

Please find the code below,

package in.prolearn.testcases;

import java.util.concurrent.TimeUnit;
import org.openqa.selenium.WebDriver;
import org.testng.annotations.BeforeMethod;
import org.testng.annotations.BeforeTest;
import org.testng.annotations.Test;

import in.prolearn.pages.HomePage;
import in.prolearn.pages.SearchResultPage;
import in.prolearn.utility.BrowserSelection;

public class VerifySnapDealSelection {
    WebDriver driver = null;

    @BeforeTest
    public void preCondition(){
        driver = BrowserSelection.browserSelection("Chrome");
        BrowserSelection.openBrowser("https://www.snapdeal.com/");
    }

    HomePage hp = new HomePage(driver);
    SearchResultPage srp = new SearchResultPage(driver);

    @Test
    public void NavigateToSearchCategoryPage() throws InterruptedException{
        hp.menuSelectionGeneric("Computers & Gaming");
        Thread.sleep(5000);
        hp.subMenuSelectionGeneric("External Hard Drives");
        Thread.sleep(5000);
    }
    @Test
    public void SearchResultPageValidation() throws InterruptedException{
        srp.FirstcapacitySelection("1 TB");
        Thread.sleep(5000);
        driver.manage().timeouts().implicitlyWait(20, TimeUnit.SECONDS);
        srp.FirstcapacitySelection("2 TB");
        Thread.sleep(5000);
        srp.verifySelectedItem("1 TB");
        srp.verifySelectedItem("2 TB");
        Thread.sleep(5000);
        srp.DeleteSelectedItem("2 TB");
        Thread.sleep(5000);
        srp.VerifycapacitySelection("2 TB", "false");
        srp.VerifyItem("1 TB", "1TB");
        srp.DeleteSelectedItem("1 TB");
        Thread.sleep(5000);
        srp.VerifycapacitySelection("1 TB", "false");
    }
}