After instantianting gameobjects, unity cant asign references anymore

Questions & Answers
1

Basically, I am making a game where you run over chicken with a car, I have everything done, EXCEPT, the spawning script.
To spawn chickens I use this script:
using UnityEngine;
using System.Collections;

public class Spawener_Chicken : MonoBehaviour
{
    public GameObject Chicken;
    public int xPos;
    public int zPos;
    public int enemyCount;
    public int enemyLimit = 100;

    
    void Start()
    {
        StartCoroutine(EnemySpawn());
    }
    void Update()
    {
       
    }
    IEnumerator EnemySpawn()
    {
        while (enemyCount < enemyLimit)
        {
            xPos = Random.Range(-30, 30);
            zPos = Random.Range(-22, 22);
            Instantiate(Chicken, new Vector3(xPos, 1, zPos), Quaternion.identity);
            yield return new WaitForSeconds(0.1f);
            enemyCount += 1;   
        } 
        while (enemyCount >= enemyLimit)
        {
            StartCoroutine(EnemySpawn());
        }
    }

}

After spawning some, Unity starts giving out errors and pausing the game.
This Is the error:

NullReferenceException: Object reference not set to an instance of an object
chicken.OnTriggerEnter (UnityEngine.Collider hit) (at Assets/scripts/chicken.cs:60)

And This is the Chicken code:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.AI;

public class chicken : MonoBehaviour
{
   private NavMeshAgent NMA;
    public int testint1 = 99;
    public int testint2;
   private GameObject Visuals;
   private GameObject ParticleSys;
    public GameObject NumberBoy;
    public Spawener_Chicken SpawnerCode;
    void Start()
    {
        StartCoroutine(wait());
    }

    void RealStart()
    {
        NumberBoy = GameObject.Find("/Car/Spawner for enemys");
        SpawnerCode = NumberBoy.GetComponent<Spawener_Chicken>();
        InvokeRepeating("ChangeDestination", 0, 5);
        NMA = GetComponent<NavMeshAgent>();
        Visuals = this.gameObject.transform.GetChild(0).gameObject;
        ParticleSys = this.gameObject.transform.GetChild(1).gameObject;
    }

    IEnumerator wait()
    {
        yield return new WaitForSeconds(1);

        RealStart();
    }

    public Vector3 RandomNavmeshLocation(float radius)
    {
        Vector3 randomDirection = Random.insideUnitSphere * radius;
        randomDirection += transform.position;
        NavMeshHit hit;
        Vector3 finalPosition = Vector3.zero;
        if (NavMesh.SamplePosition(randomDirection, out hit, radius, 99999999))
        {
            finalPosition = hit.position;
        }
        return finalPosition;
    }
    void ChangeDestination()
    {
       // Debug.Log("Changed destination");
        NMA.SetDestination(RandomNavmeshLocation(testint1));
    }

    private void OnTriggerEnter(Collider hit)
    {
        if (hit.gameObject.tag == "Car")
        {
            testint1 = 0;
            Visuals.SetActive(false);
            ParticleSys.SetActive(true);
           SpawnerCode.enemyCount--;
            //  Debug.Log(gameObject.name + ": THat GUY JUST HIT ME!");
            Destroy(gameObject, 2);
        }

        if (hit.gameObject.tag == "Destroying Wall")
        {
            SpawnerCode.enemyCount--;
            Destroy(gameObject, 0);
        }

    }
  
}
2

Hello!
There is such problem in you spawner script that you need to move the StartCoroutine line out from while loop. Because now while loop causes almost endless loop. Like this:

IEnumerator EnemySpawn()
     {
         while (enemyCount < enemyLimit)
         {
             xPos = Random.Range(-30, 30);
             zPos = Random.Range(-22, 22);
             Instantiate(Chicken, new Vector3(xPos, 1, zPos), Quaternion.identity);
             yield return new WaitForSeconds(0.1f);
             enemyCount += 1;   
         } 
         // This line is not inside while loop
         StartCoroutine(EnemySpawn());
     }

Secondary, that error that unity log gives to you causes because your variable ‘Visuals’ are null or undefined.