Stuck on getting the selected object to destroy itself when colliding with another

I am unable to get the obstacle object I want to destroy itself whenever it touches the main character of the game. I am used what I have learned from the endless runner tutorial and built my own variant based around that. Each time I try any other work around, I keep on getting a NullException error and I get lost each time. The code is below this message. Any help will be greatly appreciated.

Code (CSharp):

1. [code=CSharp]using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. using UnityEngine.SceneManagement;
5.  
6. public class DogPlayerController : MonoBehaviour
7. {
8.     // variables responsible for Jumping in the game
9.     public float jumpStrength = 10;
10.     public float gravityForce;
11.     public bool grounded = true;
12.     private float dogHealthCounter = 5;
13.     private float dogHealth = 100;
14.     private float playerWater = 1;
15.  
16.     // Variables for the other componets for the dog
17.     private Rigidbody rigidBody;
18.     private Animator dogAnimation;
19.     public ParticleSystem dogDustParticle;
20.     public bool gameOver;
21.     private GameObject _dogplayer = new GameObject();
22.  
23.     // Variables to stop the nonsense with the Nullexpection error
24.     private GameObject hazard = new GameObject();
25.     private Transform finder;
26.     private GameObject jackson = new GameObject();
27.  
28.     // Variables to make the object for the ItemSpawner class
29.     ItemSpawner item = new ItemSpawner();
30.  
31.     // Start is called before the first frame update
32.     void Start()
33.     {
34.         rigidBody = GetComponent<Rigidbody>();
35.         dogAnimation = GetComponent<Animator>();
36.         Physics.gravity *= gravityForce;
37.     }
38.  
39.     // Update is called once per frame
40.     void Update()
41.     {
42.         // when you press the spacebar to jump
43.         if(Input.GetKeyDown(KeyCode.Space) && grounded && !gameOver)
44.         {
45.             rigidBody.AddForce(Vector3.up * jumpStrength, ForceMode.Impulse);
46.             dogAnimation.SetTrigger("Arm_Dog|Jumped");
47.             grounded = false;
48.             dogDustParticle.Stop();
49.         }
50.     }
51.  
52.     private void OnCollisionEnter(Collision collision)
53.     {
54.         if(collision.gameObject.CompareTag("Ground"))
55.         {
56.             grounded = true;
57.             dogDustParticle.Play(); // Alaways call the play method when you are needing to use the items like dust particles
58.         } else if(collision.gameObject.CompareTag("Obstacle"))
59.         {
60.             jackson = hazard.transform.Find("Obstacle").gameObject;
61.             item.OnCollisionEnter(collision);
62.             _dogplayer.GetComponent<DogHealth>().gameDamage(15);
63.         } else if (collision.gameObject.CompareTag("Water"))
64.         {
65.             // code to refill health for the player
66.             jackson = hazard.transform.Find("Water").gameObject;
67.             _dogplayer.GetComponent<DogHealth>().healthIncrease(10);
68.         } else if (collision.gameObject.CompareTag("Obstacle") && dogHealth == 0)
69.         {
70.             gameOver = true;
71.             dogAnimation.SetBool("Arm_Dog|Sitting 0", true);
72.             dogDustParticle.Stop();
73.             SceneManager.LoadScene("Game Over", LoadSceneMode.Additive);
74.         }
75.     }
76. }
77.  
78.  

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class ItemSpawner : MonoBehaviour
6. {
7.     // Variables for the spawner
8.     public GameObject prefab;
9.     private Vector3 spawnPos = new Vector3(1409, 49, 426);
10.     private float startUpDelay = 4;
11.     private float repeatingRate = 15;
12.     private DogPlayerController playerControllerScript;
13.     private new Rigidbody rigidbody;
14.  
15.     // Start is called before the first frame update
16.     void Start()
17.     {
18.         rigidbody = GetComponent<Rigidbody>();
19.         playerControllerScript = GameObject.Find("DogPlayer").GetComponent<DogPlayerController>();
20.         InvokeRepeating("SpawnObstacles", startUpDelay, repeatingRate);
21.     }
22.  
23.     // Let the rigidbody take control and detect collisions.
24.     void EnableRagdoll()
25.     {
26.         rigidbody.isKinematic = false;
27.         rigidbody.detectCollisions = true;
28.     }
29.  
30.     public ItemSpawner()
31.     {
32.  
33.     }
34.  
35.     // Update is called once per frame
36.     void Update()
37.     {
38.      
39.     }
40.  
41.     void SpawnObstacles()
42.     {
43.         // Creates zero obstacles
44.         if (playerControllerScript.gameOver == false)
45.         {
46.             Instantiate(prefab, spawnPos, prefab.transform.rotation); // sets things up at the spawn position
47.         }
48.  
49.     }
50.  
51.     // Code to destroy this object upon collision
52.     public void OnCollisionEnter(Collision collision)
53.     {
54.         if (collision.gameObject.CompareTag("DogPlayer"))
55.         {
56.             Destroy(gameObject);
57.         } else if (collision.gameObject.CompareTag("HuskyDog"))
58.         {
59.             GameObject fences = collision.gameObject;
60.             Destroy(gameObject);
61.         }
62.     }
63. }

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