Ошибка в юнити шутер 2д

помогите плиз исправить ошибку
NullReferenceException: Object reference not set to an instance of an object
Shield.Update () (at Assets/Scripts/Shield.cs:29)

код щита:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;



public class Shield : MonoBehaviour
{
public float cooldown;

[HideInInspector] public bool isCooldown;

private Image shieldImage;
private Player player;
// Start is called before the first frame update
void Start()
{
shieldImage = GetComponent<Image>();
player = GameObject.FindGameObjectWithTag("Player").GetComponent<Player>();
isCooldown = true;
}

// Update is called once per frame
void Update()
{
if(isCooldown)
{
shieldImage.fillAmount -= 1 / cooldown * Time.deltaTime;
if(shieldImage.fillAmount <= 0)
{
shieldImage.fillAmount = 1;
isCooldown = false;
player.shield.SetActive(false);
gameObject.SetActive(false);
}
}

}
public void ResetTimer()
{
shieldImage.fillAmount = 1;
}
public void ReduceTime(int damage)
{
shieldImage.fillAmount += damage / 7f;
}
}