Instantiate, null reference and Raycasting problem. 2D

So, i have a 2D zombie character that checks his facing direction using raycast and detecting using 4 different colliders around the raycast's starting point. The problem is when I instantiate the prefab, it gave me a null reference to the collider detection method which I created. The script is:

 void checkDirection(Vector2 direction, Transform transform)
 {

     RaycastHit2D directionHit = Physics2D.Raycast(transform.position, direction * 10);
     if (directionHit.collider.name == "left_Colliders")
     {
         attackDirection = 3;
         faceDirection = 3;
     }
     if (directionHit.collider.name == "right_Collider")
     {
         attackDirection = 4;
         faceDirection = 4;
     }
     if (directionHit.collider.name == "up_Collider")
     {
         attackDirection = 1;
         faceDirection = 1;
     }
     if (directionHit.collider.name == "down_Collider")
     {
         attackDirection = 2;
         faceDirection = 2;
     }
 }
 private void Update()
 {
     checkDirection(direction, this.transform);

 }

which was called in the update function.

The code above was attached to my zombie main game object. There is one child collider containing 4 other child colliders to detect the 4 sides named left_colliders, right_colliders... so on.

The directions work fine. I have an empty game object with spawning enemy script attached to it:

 public GameObject enemyPrefab;

 public float full_range = 50f;

 private Transform player;

 private float playerMinX;
 private float playerMaxX;
 private float playerMinY;
 private float playerMaxY;

 private Vector3 playerPosition;

 public float randomX;
 public float randomY;


 void Start()
 {
     player = GameObject.Find("Player").transform;
 }


 void Update()
 {
     playerMinX = player.position.x - full_range / 2;
     playerMaxX = player.position.x + full_range / 2;
     playerMinY = player.position.y - full_range / 2;
     playerMaxY = player.position.y + full_range / 2;

     randomX = Random.Range(playerMinX, playerMaxX);
     randomY = Random.Range(playerMinY, playerMaxY);

     playerPosition = new Vector3(randomX, randomY, 0);

     Vector3 viewPosition = Camera.main.WorldToViewportPoint(this.gameObject.transform.position);
     if (randomX > viewPosition.x + 1 && randomY > viewPosition.y + 1)
     {
         Instantiate(enemyPrefab, playerPosition, Quaternion.identity);
     }



 }

}

(ignore the fact that it is spawning every frame per second, I will fix that later this is just a test) the script above is the script spawning my enemies around my character.

Everytime I start the game, it spawns the enemies correctly and the facing directions work just fine, however it only gives me 13-21 null reference error after those numbers, it stopped giving me the errors despite the game still spawning more in.