Simple enemy kill count

Hello, i need to create a simple enemy kill count,

public class EnemyCount : MonoBehaviour {

public int enemyKill = 0;

 void Update () 
 {
     Debug.Log (enemyKill);
 }

}

I don't know how change this variable to the destruction of another object, intuitively I thought this method

This is the script of the enemy:

public class randomDirection : MonoBehaviour { public GameObject partcSplit; private float speed = 1.0f; private Vector3 direction; public EnemyCount enemyCount;

 void Start() 
 {
     direction = (new Vector3(Random.Range(-1.0f,1.0f), Random.Range(-1.0f,1.0f),0.0f)).normalized;
     transform.Rotate(direction);
     InvokeRepeating ("speedUp",0,2.0f);
     enemyCount = GetComponent<EnemyCount>();
 }
 
 void Update()
 {
     Vector3 newPos = transform.position + direction * speed * Time.deltaTime;
     rigidbody.MovePosition (newPos);

     if (!(GameObject.FindGameObjectWithTag("Player")))
         Destroy (gameObject);
 }
 
 void OnCollisionStay (Collision col)
 {
     if (col.gameObject.tag == "Muri")   
     {
         direction = col.contacts[0].normal;
         direction = Quaternion.AngleAxis(Random.Range(-70.0f, 70.0f), Vector3.forward) * direction;
         transform.rotation = Quaternion.LookRotation(direction);
     }
     else 
     {
         Destroy (gameObject);
         Instantiate (partcSplit, transform.position, Quaternion.Euler (-90,0,0));
     }
 }
 void OnCollisionEnter (Collision col)
 {
     if (!(col.gameObject.tag == "Muri"))  
     {
         Destroy (gameObject);
         Instantiate (partcSplit, transform.position, Quaternion.Euler (-90,0,0));
         enemyCount.enemyKill++;
     }
 }

 void speedUp ()
 {
     if (speed < 15)
     speed += 1;
 }

}

but it is wrong, in fact I have an error : NullReferenceException: Object reference not set to an instance of an object.

how can i fix it?