Getting this Error : java.lang.IllegalArgumentException: Keys to send should be a not null CharSequence. How to resolve this issue?

POM design model used using TestNG Framework

Please find out the below code snippets for both the java classes I have added

The below code snippet is LoginPageTest Java Class

package com.crm.qa.testcases; 

import org.testng.Assert;
import org.testng.annotations.AfterMethod;
import org.testng.annotations.BeforeMethod;
import org.testng.annotations.Test;

import com.crm.qa.base.TestBase;
import com.crm.qa.pages.HomePage;
import com.crm.qa.pages.LoginPage;

public class LoginPageTest extends TestBase{

    LoginPage loginpage;
    HomePage homepage;

    public LoginPageTest() {
        super();
    }

    @BeforeMethod
    public void setup() {
        initialization();
        loginpage = new LoginPage();
    }

     @Test(priority=1)
     public void loginpagetitletest() {
     String title = loginpage.ValidatePageTitle();
    Assert.assertEquals(title, "Login");
    } 

    @Test(priority=2)
    public void loginTest()
    {
        homepage = loginpage.login(prop.getProperty("emailId"),prop.getProperty("password"));
    }

    @AfterMethod
    public void Teardown() {
        driver.quit();
    }

}

And the below snippet is LoginPage Java Class

package com.crm.qa.pages;

import org.openqa.selenium.By;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.interactions.Actions;
import org.openqa.selenium.support.FindBy;
import org.openqa.selenium.support.PageFactory;

import com.crm.qa.base.TestBase;

public class LoginPage extends TestBase {

    //Page Factory - object repository:

        @FindBy(id = "li_myaccount")
        WebElement myaccountbtn;

        //*[@id="li_myaccount"]/ul/li[1]/a

        @FindBy(xpath = "//a[contains(text(), 'login')]")
        WebElement loginbtn;

        @FindBy(name = "username")
        WebElement username;

        @FindBy(name = "password")
        WebElement password;

        @FindBy(xpath = "//*[@id='loginfrm']/button")
        WebElement lgnbtn;

        @FindBy(xpath = "//a[contains(text(), 'Sign Up')]")
        WebElement Signupbtn;

        //Initialize the Page Objects
    public LoginPage() {
        PageFactory.initElements(driver, this);
    }

    //Actions
    public String ValidatePageTitle() {
        return driver.getTitle();
    }


    public HomePage login(String un, String pwd) {

        username.sendKeys(un);
        password.sendKeys(pwd);
        myaccountbtn.click();
        loginbtn.click();

        return new HomePage();
        }

    } package com.crm.qa.pages;

import org.openqa.selenium.By;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.interactions.Actions;
import org.openqa.selenium.support.FindBy;
import org.openqa.selenium.support.PageFactory;

import com.crm.qa.base.TestBase;

public class LoginPage extends TestBase {

    //Page Factory - object repository:

        @FindBy(id = "li_myaccount")
        WebElement myaccountbtn;

        //*[@id="li_myaccount"]/ul/li[1]/a

        @FindBy(xpath = "//a[contains(text(), 'login')]")
        WebElement loginbtn;

        @FindBy(name = "username")
        WebElement username;

        @FindBy(name = "password")
        WebElement password;

        @FindBy(xpath = "//*[@id='loginfrm']/button")
        WebElement lgnbtn;

        @FindBy(xpath = "//a[contains(text(), 'Sign Up')]")
        WebElement Signupbtn;

        //Initialize the Page Objects
    public LoginPage() {
        PageFactory.initElements(driver, this);
    }

    //Actions
    public String ValidatePageTitle() {
        return driver.getTitle();
    }


    public HomePage login(String un, String pwd) {

        username.sendKeys(un);
        password.sendKeys(pwd);
        myaccountbtn.click();
        loginbtn.click();

    return new HomePage();
        }

    }`