C# Unity Object reference not set to an instance of an object

Question

I m trying to acces gamemanger function via : `else if(col.tag == "Arrow") { FindObjectOfType().EndGame();

    }`

and every time show me the error : Object reference not set to an instance of an object Arrow.OnTriggerEnter2D (UnityEngine.Collider2D col) (at Assets/Scripts/Arrow.cs:38)

How can i fix it?

Here is the GameManager code :

using System.Collections;

using System.Collections.Generic; using UnityEngine;

public class GameManager : MonoBehaviour {

private bool gameHasEnded = false;

public Circle circle;
public Spawner spawner;


public void EndGame()
{
    if (gameHasEnded)
        return;

    circle.enabled = false;
    spawner.enabled = false;

    

    gameHasEnded = true;
}

}