Need help rotating a game object to the position of another

Some background information: I am following a tutorial by popular unity youtuber Brackeys. I have followed it very closely (it is how to make a tower defense game) although I am running into the issue that although the debug.logs are telling me that everything is working, I get the error "NullReferenceException: Object reference not set to an instance of an object" and says the error is on line 54. The turret is also not rotating to the oncoming enemies position. Full code below:

Code (CSharp):

1. using UnityEngine;
2. using System.Collections;
3.  
4. public class Turret : MonoBehaviour
5. {
6.  
7.     private Transform target;
8.     public float range = 15f;
9.  
10.     public string enemyTag = "Baddy";
11.  
12.     public Transform partToRotate;
13.  
14.     private void Start()
15.     {
16.         InvokeRepeating("UpdateTarget", 0f, 0.5f);
17.     }
18.  
19.     void UpdateTarget()
20.     {
21.         GameObject[] enemies = GameObject.FindGameObjectsWithTag(enemyTag);
22.         float shortestDistance = Mathf.Infinity;
23.         GameObject nearestEnemy = null;
24.         //Debug.Log("Looking!");
25.  
26.         foreach (GameObject enemy in enemies)
27.         {
28.             //Debug.Log("checking");
29.             float distanceToEnemy = Vector3.Distance(transform.position, enemy.transform.position);
30.             if(distanceToEnemy < shortestDistance)
31.             {
32.                 shortestDistance = distanceToEnemy;
33.                 nearestEnemy = enemy;
34.                 //Debug.Log("its close!");
35.             }
36.         }
37.  
38.         if(nearestEnemy != null && shortestDistance <= range)
39.         {
40.             target = nearestEnemy.transform;
41.             //Debug.Log("I see an enemy!");
42.         }
43.         else
44.         {
45.             target = null;
46.         }
47.     }
48.  
49.     private void Update()
50.     {
51.         if (target = null)
52.             return;
53.  
54.         Vector3 dir = target.position - transform.position;
55.         Quaternion lookRotation = Quaternion.LookRotation(dir);
56.         Vector3 rotation = lookRotation.eulerAngles;
57.         partToRotate.rotation = Quaternion.Euler(0f, rotation.y, 0f);
58.  
59.     }
60.  
61.     private void OnDrawGizmosSelected()
62.     {
63.         Gizmos.color = Color.red;
64.         Gizmos.DrawWireSphere(transform.position, range);
65.     }
66. }
67.  

THANKS FOR ANY HELP!

 

On line 51, you have "if (target = null)", but you probably mean "if (target == null)", with two equals signs.

== means test if two things are equal
= means make them equal

 

Your mistake is on line 51, you are using an assignment operator =, rather than a comparison ==. Also, not a fan of that return to "break" from the Update(), simply do, instead : if (target != null) {//Rest of the Update() code.}

 

THANK YOU