"NullReferenceException: Object reference not set to an instance of an object" in LevelController.

Unity Engine
1

Hello all! I’m currently having a problem with my code that is disallowing me from playing my currently set scene, named Level1, and instead returning with a “NullReferenceException: Object reference not set to an instance of an object” error in the console window while automatically switching to Level2 and messing up a bunch of the GameObjects.

Currently my code is reading the following:

Enemy.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

[RequireComponent(typeof(AudioSource))]
public class Enemy : MonoBehaviour
{
    [SerializeField] public GameObject _cloudParticlePrefab;
    public AudioClip pop;
    AudioSource audioSource;

    void Start()
    {
        audioSource = GetComponent<AudioSource>();
    }

    public void OnCollisionEnter2D(Collision2D collision)
    {

        Bird bird = collision.collider.GetComponent<Bird>();
        if (bird != null)
        {
            audioSource.clip = pop;
            audioSource.PlayOneShot(pop, 0.7F);
            Instantiate(_cloudParticlePrefab, transform.position, Quaternion.identity);
            Destroy(gameObject, 0.1F);
            return;
        }

        Enemy enemy = collision.collider.GetComponent<Enemy>();
        if (enemy != null)
        {
            return;
        }

        if (collision.contacts[0].normal.y < -0.5)
        {
            audioSource.clip = pop;
            audioSource.PlayOneShot(pop, 0.7F);
            Instantiate(_cloudParticlePrefab, transform.position, Quaternion.identity);
            Destroy(gameObject, 0.1F);
            return;
        }
    }
}

Bird.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.SceneManagement;

public class Bird : MonoBehaviour
{
    Vector3 _initialPosition;
    private bool _birdWasLaunched;
    private float _timeSittingAround;

    [SerializeField] private float _launchPower = 350;

    private void Awake()
    {
        _initialPosition = transform.position;
    }

    private void Update()
    {
        GetComponent<LineRenderer>().SetPosition(0, transform.position);
        GetComponent<LineRenderer>().SetPosition(1, _initialPosition);

        if (_birdWasLaunched &&
        GetComponent<Rigidbody2D>().velocity.magnitude <= 0.1)
        {
            _timeSittingAround += Time.deltaTime;
        }

        if (transform.position.y > 10 ||
        transform.position.y < -10 ||
        transform.position.x > 20 ||
        transform.position.x < -20 ||
        _timeSittingAround > 3)
        {
            string currentSceneName = SceneManager.GetActiveScene().name;
            SceneManager.LoadScene(currentSceneName);
        }
    }

    private void OnMouseDown()
    {
        GetComponent<SpriteRenderer>().color = Color.red;
        GetComponent<LineRenderer>().enabled = true;
    }

    private void OnMouseUp()
    {
        GetComponent<SpriteRenderer>().color = Color.white;

        Vector2 directionToInitialPosition = _initialPosition - transform.position;
        
        GetComponent<Rigidbody2D>().AddForce(directionToInitialPosition * _launchPower);
        GetComponent<Rigidbody2D>().gravityScale = 1;
        _birdWasLaunched = true;
        
        GetComponent<LineRenderer>().enabled = false;
    }

    private void OnMouseDrag()
    {
        Vector3 newPosition = Camera.main.ScreenToWorldPoint(Input.mousePosition);
        transform.position = new Vector3(newPosition.x, newPosition.y);
    }
}

LevelController.cs

using UnityEngine;
using UnityEngine.SceneManagement;

public class LevelController : MonoBehaviour
{
    public static int _nextLevelIndex = 1;
    public Enemy[] _enemies;

    public void onEnable()
    {
        _enemies = FindObjectsOfType<Enemy>();
    }

    // Update is called once per frame
    void Update()
    {
        foreach(Enemy enemy in _enemies)
        {
            if (enemy != null)
                return;
        }

        Debug.Log("You killed all enemies!");
      
        _nextLevelIndex++;
        string nextLevelName = "Level" + _nextLevelIndex;
        SceneManager.LoadScene(nextLevelName);

    }
}

The LevelController.cs file at line 17 is where I’m having the troubles. The error reads in the console like this…

LevelController.Update () (at Assets/LevelController.cs:17)```

I guess the real question here is, can y'all help me identify where the problem is in the code and help me correct it?

Thank you!

P.S. I think it's worth saying that the function to switch scenes is working just fine, it's the error code and the timing of the switching of scenes that gets me. Also, I have correctly added all the scripts to their respective GameObjects, so that isn't the problem.
2

I’m using the 2019.4.13f1 LTS build of Unity if that makes any difference.

3

Try changing this line

collision.collider

to

collision.gameObject.collider

4

I’ve solved the error problem, but the scene still aren’t changing.

UPDATED CODE:

using UnityEngine;
using UnityEngine.SceneManagement;

public class LevelController : MonoBehaviour
{
    public static int _nextLevelIndex = 1;
    public Enemy[] _enemies;

    public void onEnable()
    {
        _enemies = FindObjectsOfType<Enemy>();
    }

    public void Start()
    {
        _nextLevelIndex++;
        string nextLevelName = "Level" + _nextLevelIndex;
        foreach(Enemy enemy in _enemies)
        {
            if (enemy == null)
            {
                Debug.Log("You killed all enemies!");
                SceneManager.LoadScene(nextLevelName);
            }
        }
    }

    // Update is called once per frame
    public void Update()
    {
        foreach(Enemy enemy in _enemies)
        {
            if (enemy != null)
                return;
        }
       
       
    }
   
}
5

It seems as though collision.gameObject.collider was deprecated. Don’t know why, I’m just going off of what VSCode tells me.

6

Why are you trying to change the scene in Start? If there are no enemies then it will immediately change to the next scene. Also, you need to make onEnable function OnEnable. That capital O is important.