How do i remove a like from a photo in my code

I have written a program for a photo upload site where users can like photos, I have a test script to like the photo then display all the likes then i want to remove the like and display all the likes now. How do i do this?

import java.util.*;

public class Likes {
    private static Hashtable<Photo, TreeSet<User>> likes = new Hashtable<>();

    //like photo
    public static void like(Photo photo, User user) {
        try {
            likes.get(photo).add(user);
        }
        catch (NullPointerException e) {
            likes.put(photo, new TreeSet<>());
            likes.get(photo).add(user);
        }
    }



    //unlike photo
    public static void unlike(Photo photo, User user) {
        try {
            likes.get(photo.remove(user));
        }
        catch (NullPointerException e) {

        }
    }

    //has liked photo
    public boolean hasliked(Photo photo, User user) {
        try {
            return likes.get(photo).contains(user);
        }
        catch (NullPointerException e) {
            return false;
        }
    }

    //get all likes
    public List<Photo> getAllLikes(User user){
        // new empty list
        List<Photo> likedphotos = new ArrayList<Photo>();

        for (Photo photo : likes.keySet()) {
            if(hasliked(photo, user)){
                // add photo to list
                likedphotos.add(photo);
            }
            // return that initial list
        }

        return likedphotos;

    }



    public String toString() {
        return likes.toString();
    }

    public void get(Photo remove) {
    }

    public void remove(Photo photo1, User user1) {
    }
}

Tests:

import java.sql.SQLOutput;
import java.util.*;

public class TestDrive {

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



        //create 2 photo object
        Photo photo1 = new Photo();
        Photo photo2 = new Photo();

        //create 1 user object
        User user1 = new User();

        //create 1 like object
        Likes likes1 = new Likes();


        //set 2 photos
        photo1.setimageURL("photo of user 2");
        photo2.setimageURL("photo of user 1");

        //print the 2 photos
        System.out.println(photo1.getimageURL());
        System.out.println(photo2.getimageURL());


        //set 1 user
        user1.setUserName("oopnoob");

        //print the username
        System.out.println(user1.getUserName());

        //Like the 2 photos


        Likes.like(photo1, user1);
        Likes.like(photo2, user1);

        //Test the hasliked method to see if user1 has liked both photos - both should return true

        System.out.println("Should be true: " + likes1.hasliked(photo1, user1));
        System.out.println("Should be true: " + likes1.hasliked(photo2, user1));


        //Test the getAllLikes for user1. Should print 2 photos.

        System.out.println("user1 liked: " + likes1.getAllLikes(user1));


//i dont know how to remove the like from the photo

        //Test the unlike feature by unliking photo1

        likes1.unlike(photo1, user1);


        //Test the getAllLikes - should only print one photo

        System.out.println("user1 liked: " + likes1.getAllLikes(user1));







    }

}