Projectile prefabs can't read other script....

Unity Engine
,
1

Hi, I want my player object to shoot projectile and take damage to enemy when the projectile collides with the enemy.
To do this, I wrote 3 scripts ; Player, Enemy, Projectile.
However, when projectile hits the enemy, the unity editor has an error like this

“NullReferenceException: Object reference not set to an instance of an object
Projectile.OnCollisionEnter (UnityEngine.Collision collision) (at Assets/ScriptTest/Skill.cs:25)”

Please explain why it is and how to fix it.
(the codes worked out when projectile was not prefabs but just an object.)

Here is my 3 scripts

public class Player : MonoBehaviour
{
    public GameObject projectilePrefabs;
    private Rigidbody playerRb;
 

    void Start()
    {
        playerRb = GetComponent<Rigidbody>();
    }

    // Update is called once per frame
    void Update()
    {
        SpawnPrefab();
    }
    private void SpawnPrefab()
    {
        if (Input.GetKeyDown(KeyCode.Alpha1))
        {
            Instantiate(projectilePrefabs, transform.position, projectilePrefabs.transform.rotation);
        }
    }
}

public class Enemy : MonoBehaviour
{
    public int maxHealth = 10;
    private int currentHealth;
    // Start is called before the first frame update
    void Start()
    {
        currentHealth = maxHealth;
    }

    // Update is called once per frame
    void Update()
    {
   
    }
    public void TakeDamage(int amount)
    {
        currentHealth -= amount;
        Debug.Log(currentHealth);
    }
}

public class Projectile : MonoBehaviour
{
    private Rigidbody projectileRb;
    private int speed = 5;
    private Enemy enemyScript;
    void Start()
    {
        projectileRb = GetComponent<Rigidbody>();
        enemyScript = GetComponent<Enemy>();
    }

    // Update is called once per frame
    void Update()
    {
        projectileRb.transform.Translate(Vector3.forward * speed * Time.deltaTime);
    }
    private void OnCollisionEnter(Collision collision)
    {
            enemyScript.TakeDamage(1);

    }
}
2

The error is in a script called Skill.cs on line 25, which is not provided here.

3

You need to check that your projectile is colliding with an enemy. If the projectile hits any object without an Enemy script you will get an error.

Tag your enemies with tag “Enemy”

private void OnCollisionEnter(Collision collision)
        {
            if (collision.CompareTag("Enemy"))
            {
                collision.GetComponent<Enemy>().TakeDamage(30);
            }
        }