Grenade damage script error

i will grenade damage to enemies but when i write this code and throw the grenade i get this error. how can i fix this?

NullReferenceException: Object reference not set to an instance of an object ApplyDamage.Attack () (at Assets/ApplyDamage.cs:38)

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class ApplyDamage : MonoBehaviour {
     int damage = 100;
     private GameObject[] enemy;
     EnemyHealth enemyHealth;
     private bool enemyInRange;
     // Use this for initialization
     void Start () {
         GameObject[] enemy = GameObject.FindGameObjectsWithTag ("Enemy");
         foreach(GameObject enemies in enemy)
         {
             enemyHealth = enemies.GetComponent<EnemyHealth> ();
         }
     }
     void OnTriggerEnter (Collider other)
     {
             enemyInRange = true;
     }
 
     void OnTriggerExit (Collider other)
     {
             enemyInRange = false;
     }
 
     // Update is called once per frame
     void Update () {
         if (enemyInRange) {
             Attack ();
         }
     }
 
     public void Attack()
     {
         enemyHealth.TakeDamage (damage);
     }
 }