MissingReferenceException:

So I'm doing Brackys how to make a TD Game Here's the video link

here's my code

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 
 
 public class EnemyMovement : MonoBehaviour
 {
     public float speed = 1f;
 
     private Transform target;
     private int wavepointIndex = 0;
 
     void Start()    
     {
         target = Waypoints.waypoints[0];
 
     }
 
     void Update()
     {
         Vector3 dir = target.position - transform.position;
         transform.Translate(dir.normalized * speed * Time.deltaTime, Space.World);
 
         if(Vector3.Distance(transform.position, target.position) <= .2f)
         {
             getNextWaypoint();
         }
 
 
     }
 
 
     void getNextWaypoint()
     {
         if(wavepointIndex >= Waypoints.waypoints.Length - 1)
         {
             Destroy(gameObject);
             return;
         }
 
         wavepointIndex++;
         target = Waypoints.waypoints[wavepointIndex];
     }
 }
 

MissingReferenceException: The object of type 'Transform' has been destroyed but you are still trying to access it. Your script should either check if it is null or you should not destroy the object

I don't know what's wrong with it. and here is the whole error.

MissingReferenceException: The object of type 'Transform' has been destroyed but you are still trying to access it.



Your script should either check if it is null or you should not destroy the object. UnityEngine.Object.Internal_InstantiateSingle (UnityEngine.Object data, UnityEngine.Vector3 pos, UnityEngine.Quaternion rot) (at :0) UnityEngine.Object.Instantiate (UnityEngine.Object original, UnityEngine.Vector3 position, UnityEngine.Quaternion rotation) (at :0) UnityEngine.Object.Instantiate[T] (T original, UnityEngine.Vector3 position, UnityEngine.Quaternion rotation) (at :0) WaveSpawner.SpawnEnemy () (at Assets/WaveSpawner.cs:54) WaveSpawner+d__7.MoveNext () (at Assets/WaveSpawner.cs:44) UnityEngine.SetupCoroutine.InvokeMoveNext (System.Collections.IEnumerator enumerator, System.IntPtr returnValueAddress) (at :0)

Then here's the code that's it's pointing to

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 
 public class WaveSpawner : MonoBehaviour
 {
 
     public Transform enemyPrefab;
     public Transform spawnPoint;
 
 
     public float timeBetweenWaves = 5f;
     private float countdown = 2f;
 
     private int waveIndex = 0;
 
     public Text waveCountdownText;
 
 
     void Update()
     {
         if(countdown <= 0f)
         {
             StartCoroutine(SpawnWave());
             countdown = timeBetweenWaves;
 
         }
 
         countdown -= Time.deltaTime;
 
         waveCountdownText.text = Mathf.Floor(countdown).ToString();
 
 
 
 
     }
 
     IEnumerator SpawnWave()
     {
         waveIndex++;
         for (int i = 0; i < waveIndex; i++)
         {
             SpawnEnemy();
             yield return new WaitForSeconds(.5f);
         }
        
     }
 
     void SpawnEnemy()
     {
             Instantiate(enemyPrefab, spawnPoint.position, spawnPoint.rotation);
     }
 }
 

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