Unable to make enemy affect player since the object isn't set to reference

I'm working on a small game project where an enemy is moving towards the player. Coming in contact with the enemy despawns the player and causes a game over. The game is pretty much functional aside from the enemy, as the player passes through the enemy rather than triggering a game over.

This is the error message I got:
NullReferenceException: Object reference not set to an instance of an object
GameManager.Start () (at Assets/Scripts/GameManager.cs:20)

It appears to be an issue in the game manager script, but I'll post the obstacle script too if that helps.

GAME MANAGER

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. using UnityEngine.UI;
5. using TMPro;
6. using UnityEngine.SceneManagement;
7.  
8. public class GameManager : MonoBehaviour
9. {
10.  
11.     public int score;
12.     public int scoreTarget;
13.     public TMP_Text scoreText;
14.     public TMP_Text winText;
15.  
16.     //***ABOVE IS FOR WIN***
17.  
18.     private void Start()
19.     {
20.         winText.gameObject.SetActive(false);
21.     }
22.  
23.     // Update is called once per frame
24.     void Update()
25.     {
26.         // If the esc key was pressed and released...
27.         if (Input.GetKeyUp(KeyCode.Escape) == true)
28.         {
29.             // Quit the game (only works with built games)
30.             Application.Quit();
31.         }
32.  
33.         //****BOTTOM CODE RELOADS A SCENE AFTER WINNING****
34.         if (Input.GetKeyUp(KeyCode.Space) == true)
35.         {
36.             // Reload the scene
37.             SceneManager.LoadScene(SceneManager.GetActiveScene().buildIndex);
38.         }
39.  
40.  
41.     }
42.  
43.     //****USE FOR GAME OVER****
44.     public void Lose()
45.     {
46.         winText.gameObject.SetActive(true);
47.         winText.text = "THERE IS NO ESCAPE\npress space to restart";
48.     }
49. }

ENEMY/OBSTACLE

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. using UnityEngine.SceneManagement;
5.  
6. public class ObstacleCheck : MonoBehaviour
7. {
8.     private float dirX;
9.     private float moveSpeed;
10.     private Rigidbody2D rb;
11.     private Vector3 localScale;
12.  
13.     void Start()
14.     {
15.         localScale = transform.localScale;
16.         rb = GetComponent<Rigidbody2D>();
17.         dirX = 1f;
18.         moveSpeed = 3f;
19.     }
20.  
21.     private void OnCollisionEnter2D(Collision2D collision)
22.     {
23.         if (collision.gameObject.tag == "Player")
24.         {
25.             SceneManager.LoadScene(SceneManager.GetActiveScene().name);
26.         }
27.     }
28.  
29.     void FixedUpdate()
30.     {
31.         rb.velocity = new Vector2(dirX * moveSpeed, rb.velocity.y);
32.     }
33. }

 

It actually doesn't even matter what you're doing or what code you post.

The answer is always the same.

How to fix a NullReferenceException error

https://forum.unity.com/threads/how-to-fix-a-nullreferenceexception-error.1230297/

Steps to success:
- Identify what is null
- Identify why it is null
- Fix that

 

A little confused on how I should break down the hairy code that's causing the problems. The example provided is a bit different to what my problematic code line is (I think it's 20 judging by the error message, but I could be wrong)

 

Did you put a Debug.Log() immediately prior to the scene load to see what string you're ultimately giving it?