Help Enemies don't move

Getting Started
1

I’m working through Challenge 4 - Soccer Scripting - Unity Learn task 7 to get enemies to move towards players goal. I’ve added the player goal in the inspector. The scripts I’m using is this.

public class EnemyX : MonoBehaviour
{
    public float speed;
    private Rigidbody enemyRb;
    public GameObject playerGoal;

    // Start is called before the first frame update
    void Start()
    {
        enemyRb = GetComponent<Rigidbody>();
        playerGoal = GameObject.Find("PlayerGoal");
    }

    // Update is called once per frame
    void Update()
    {
        // Set enemy direction towards player goal and move there
        Vector3 lookDirection = (playerGoal.transform.position - transform.position).normalized;
        enemyRb.AddForce(lookDirection * speed);

    }

    private void OnCollisionEnter(Collision other)
    {
        // If enemy collides with either goal, destroy it
        if (other.gameObject.name == "Enemy Goal")
        {
            Destroy(gameObject);
        }

With this script the enemies won’t move unless the player hits them then its random slow movement. I get an error message saying “NullReferenceException: Object reference not set to an instance of an object” which I assume means I haven’t added the player goal into the inspector. But I have, but when I press play it disappears.

If I delete the " playerGoal = GameObject.Find(“PlayerGoal”);" from the start the first enemy moves towards goal as it should but then the next wave of enemies don’t move and the inspector area goes blank. I have put it so prefabs behave same way as origional enemy.

If I double click the error message it highlights this line.
Vector3 lookDirection = (playerGoal.transform.position - transform.position).normalized;

2

If you get a null reference error, it means some reference you’re using is not set. You didn’t mention which line of the code you’re getting that error, which is in the error message and the most important information. After you hit a null reference error, none of the code which follows that error is run.

A quick look at the code, you likely have playerGoal or enemyRb as null. If it is enemyRb, that means that the GetComponent call in Start is failing (probably because there is no Rigidbody component attached to this GameObject). If it is playerGoal, then the Find call in Start is failing (which means there is no GameObject with the exact name “PlayerGoal” in the scene hierarchy). It being in the inspector before you hit Play is meaningless, because you are setting it again in Start, which overwrites whatever is there.

You can check if a reference is null in code, and add Debug.Log messages to help figure it out. Then just check the console window.

void Start()
{
    enemyRb = GetComponent<Rigidbody>();
    if (enemyRb == null)
    {
        Debug.Log("enemyRb is null);
    }
    playerGoal = GameObject.Find("PlayerGoal");
    if (playerGoal == null)
    {
        Debug.Log("playerGoal is null");
    }
}