Unity 3D : NullReferenceException with Player health

Question

I'm a beginner developper and I just started making my own game but in my advancement I got stuck with the creation of an enemy.

The goal of this script is to move the enemy, catch the player and most of all making damages to the player, but in this case, I cannot make link between my player health and my enemy controller script because of the NullReferenceException error that haunts me. It's the only error I have and I've searched everywhere to fix my error but don't find anything.

This is my EnemyController script which I know is not really optimized but whatever. The real problem is right here at the line 49 in the Update function (if(playerHealth == null){})
All of my scripts are connected, here are all scripts I used for this.

using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.AI;

public class EnemyContoller : MonoBehaviour
{
    public float lookRadius = 10f;
    public float maxHealth = 100f;
    public float currentHealth;
    Transform target;
    NavMeshAgent agent;
    public HealthBarScript healthBar;
    public Animator anim;
    EnemyAttack attack;
    PlayerHealth playerHealth;

    // Update is called once per frame
    void Start()
    {
        attack = GetComponent<EnemyAttack>();
        anim = GetComponent<Animator>();
        gameObject.layer = 6;
        currentHealth = maxHealth;
        healthBar.SetMaxHealth(maxHealth);
        target = PlayerManager.instance.player.transform;
        agent = GetComponent<NavMeshAgent>();
        playerHealth = GetComponent<PlayerHealth>();
    }
    
    void Update()
    {
        float distance = Vector3.Distance(target.position, transform.position);

        if(distance <= lookRadius)
        {
            anim.speed = agent.speed;
            anim.SetBool("isRunning",true);
            agent.SetDestination(target.position);
        }else{
            anim.speed = 0;
            anim.SetBool("isRunning",false);
        }

        if(distance <= agent.stoppingDistance)
        {
            if(playerHealth != null)
            {
                attack.MakeDamage(attack.damages, playerHealth);
                Debug.Log(playerHealth.currentHealth);
            }
            else if(playerHealth == null)
            {
                Debug.Log("Player Health = null");
            }
            FaceTarget();
        }
    }

    public void TakeDamage(float amount){
        currentHealth -= amount;
        healthBar.SetHealth(currentHealth);
        if(currentHealth <= 0)
        {
            Die();
        }
    }
    void Die()
    {
        Destroy(gameObject);
    }

    void OnDrawGizmosSelected()
    {
        Gizmos.color = Color.red;
        Gizmos.DrawWireSphere(transform.position, lookRadius);
    }

    void FaceTarget()
    {
        Vector3 direction = (target.position - transform.position).normalized;
        Quaternion lookRotation = Quaternion.LookRotation(new Vector3(direction.x, 0, direction.z));
        transform.rotation = Quaternion.Slerp(transform.rotation, lookRotation, Time.deltaTime * 3f);
    }
}

This is my Enemy Attack script

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

public class EnemyAttack : MonoBehaviour
{
    public float damages = 10f;
    public float damageRate = 1f;
    private float damageCooldown = 0f;
    PlayerHealth pH;

    void Update()
    {
        damageCooldown -= Time.deltaTime;
    }
    public void MakeDamage(float amount, PlayerHealth health)
    {
        if(damageCooldown <= 0f)
        {
            pH.TakeDamage(damages);
            Debug.Log(health);
            damageCooldown = 1f / damageRate;
        }
    }
}

This my PlayerHealth script

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

public class PlayerHealth : MonoBehaviour
{
    public float currentHealth;
    public float maxHealth = 50f;
    public HealthBarScript healthBar;
    // Start is called before the first frame update
    void Start()
    {
        currentHealth = maxHealth;
        healthBar.SetMaxHealth(maxHealth);
    }

    public void TakeDamage(float amount)
    {
        currentHealth -= amount;
        healthBar.SetHealth(currentHealth);
        Debug.Log(currentHealth);
        if(currentHealth <= 0)
        {
            Debug.Log("You're Dead.");
            Time.timeScale = 0;
        }
    }
}

If someone could help me that would be great I don't know what to do to fix this bug that lasts for 2 days.