Zombie Spawner Not Spawn Zombies

Hello Im making a zombie game, and im trying to make a zombie spawner but the zombies wont spawn please help. Heres My Code:

using UnityEngine; using System.Collections;

public class ZombieSpawner : MonoBehaviour {

 public Transform _Zombie;
 
 public bool HasZombieSpawned = false;
 
 public float SpawnTimer = 0;
 
 public GameObject ZombiePrefab;
 
 public void Update(){
     
     if(HasZombieSpawned == false){
     
     SpawnTimer += Time.deltaTime;
         
     if(SpawnTimer == 10){
     HasZombieSpawned = true;
     GameObject SpawnedZombie = Instantiate(ZombiePrefab, Vector3.zero, Quaternion.identity) as GameObject;
     SpawnedZombie.transform.parent = gameObject.transform;
     SpawnedZombie.transform.localPosition = Vector3.zero;
     SpawnTimer = 0;
     _Zombie = SpawnedZombie.transform;
         
     }
     
     }
     
     if(_Zombie == null){
         HasZombieSpawned = false;
     }
     
 }
 

}