Object reference not set to an instance of an object

Hello everyone. I am an extremely new programmer and im following a Udemy course in development. I have added a spawn manager to the game, and ive followed to tutorial exactly, but im not sure exactly what this mean. i have done some research into the message but from (as far as i understand, and im sure im wrong) im referencing everything correctly.

This message only happens after and instantiated enemy (Enemy Clone) collides with the player. any help would be appreciated.

Debug Log Message:
NullReferenceException: Object reference not set to an instance of an object
Player.Damage () (at Assets/Script/Player.cs:94)
Enemy.OnTriggerEnter (UnityEngine.Collider other) (at Assets/Script/Enemy.cs:36)

Enemy Script
--------------------------------------------------------

Code (CSharp):

1. public class Enemy : MonoBehaviour
2. {
3.     private float x;
4.     private float y;
5.     private float z;
6.     public float EnemySpeed = 4.0f;
7.     // Start is called before the first frame update
8.     void Start()
9.     {
10.         transform.position = new Vector3 (0, 7.0f, 0);
11.        
12.     }
13.  
14.     // Update is called once per frame
15.     void Update()
16.     {
17.          x = Random.Range (-8.79f, 8.79f);
18.         transform.position += Vector3.down * EnemySpeed * Time.deltaTime;
19.          if (transform.position.y <= -5.74f)
20.     {
21.         transform.position = new Vector3 (x, 7.0f, transform.position.z);
22.    
23.     }
24.    
25.     }
26.     private void OnTriggerEnter(Collider other)
27.     {  
28.         Debug.Log("Hit: "+ other.transform.name);
29.         if (other.gameObject.CompareTag("Player"))
30.         {
31.             Player player = other.transform.GetComponent<Player>();
32.            
33.            if (player != null)
34.            {
35.                player.Damage();
36.            }
37.            Destroy(this.gameObject);
38.  
39.         }
40.        else if (other.gameObject.CompareTag("Laser"))
41.         {
42.             Destroy(this.gameObject);
43.         }
44.        }
45.    
46. }
47.  

Code (CSharp):

1. public class Player : MonoBehaviour
2. {
3.     // Start is called before the first frame update
4.     public float moveSpeed = 5.0f;
5.     [SerializeField]
6.     private GameObject Laser;
7.     private GameObject LaserClone;
8.     [SerializeField]
9.     private float fireRate = 0.5f;
10.     [SerializeField]
11.     private float nextFire = 0.0f;
12.     [SerializeField]
13.     public int playerLives = 3;
14.     [SerializeField]
15.     private int currentLives = 3;
16.     private SpawnManager _spawnManager;
17.     void Start()
18.     {
19.         //get current position. move to origin
20.         transform.position = new Vector3(0,0,0);
21.         _spawnManager = GameObject.Find("Spawn Manager").GetComponent<SpawnManager>();
22.         if(_spawnManager = null)
23.         {
24.             Debug.LogError("Spawn Manager is Null.");
25.         }
26.        
27.     }
28.  
29.     // Update is called once per frame
30.     void Update()
31.     {                   //Player controls
32.         if (Input.GetKey(KeyCode.A))
33.      transform.Translate(Vector3.left * moveSpeed * Time.deltaTime);
34.  
35.         if (Input.GetKey(KeyCode.D))
36.         transform.Translate(Vector3.right* moveSpeed * Time.deltaTime);
37.  
38.         if (Input.GetKey(KeyCode.W))
39.         transform.Translate(Vector3.up * moveSpeed * Time.deltaTime);
40.  
41.         if (Input.GetKey(KeyCode.S))
42.         transform.Translate(Vector3.down * moveSpeed * Time.deltaTime);
43.  
44.         //if player position on y is more than 0
45.         //y position = 0
46.         //this controls player bounds
47.  
48.         if (transform.position.y >= 3.70f)
49.         {
50.             transform.position = new Vector3 (transform.position.x, 3.70f, transform.position.z);
51.         }
52.         else if(transform.position.y <= -4.39f)
53.         {
54.             transform.position = new Vector3 (transform.position.x, -4.38f, transform.position.z);
55.         }
56.         if(transform.position.x <= -8.36f)
57.         {
58.             transform.position = new Vector3 (9.36f, transform.position.y, transform.position.z);
59.         }
60.         else if (transform.position.x >= 10.0f)
61.         {
62.             transform.position = new Vector3 (-8.35f, transform.position.y, transform.position.z);
63.         }
64.          if (Input.GetKeyDown(KeyCode.Space) && Time.time > nextFire)
65.        
66.          {
67.              Debug.Log("BAM!");
68.               nextFire = Time.time + fireRate;
69.               Vector3 offset = new Vector3(0,0.8f,0);
70.               LaserClone = Instantiate(Laser, transform.position + offset, Quaternion.identity);
71.               LaserClone.gameObject.tag = "Laser";
72.               Destroy(LaserClone, 3.5f);
73.            
74.            
75.          }
76.        
77.    
78.  
79.     }
80.     public void Damage()
81.     {
82.         playerLives -= 1;
83.  
84.         //check if dead
85.         //if true destroy us
86.  
87.         if(playerLives < 1)
88.         {
89.            
90.             _spawnManager.OnPlayerDeath();
91.             Destroy(this.gameObject);
92.         }
93.  
94.     }
95.      public void OnTriggerEnter(Collider other)
96.      {
97.          if(other.gameObject.CompareTag("Enemy"))
98.          currentLives =- 1;
99.          Debug.Log("Health= " + currentLives);
100.      }
101.  
102.    
103. }
104.  

 

_spawnManager is null when you do this:

Code (csharp):

1. _spawnManager.OnPlayerDeath();

Since you're checking that it's not in Start, I'm guessing that it's gotten destroyed at some point.

 

So as it turns out on my Null check in my player void Start
i had used "=" instead of "==" can anyone explain why this would make such big difference.

 

Oh, didn't spot that.

= is assignment (x = y sets x to be y), while == is an equality check (x == y checks if x is y)

 

Makes sense haha. Only took me long enough to wanna bang my head against my desk. Much appreciated bro.