Survival Shooter game object reference issue

Hello. i am currently watching the survival shooter tutorial and i was doing fine. I am following precisely the instruction and besides the fact that i am kinda new in unity , i am a bit familiar with some stuff because i already made some 2D games(with Unity). So the issue here is that the code and game was perfectly working besides some details in the animator which i fixed. I run the game and it was warking just fine. Then suddenly without doing anything, i run the game agan and it wasn't working... the enemy was chasing but did nothing else... the error was :

NullReferenceException: Object reference not set to an instance of an object CompleteProject.

which basically is weird because i triple checked it for hours. all the references and objects and tags and all of the stuff are fine. The code is copied from the tutorial. I feel like it's a bug. But i really need a second "eye" on that to make sure it's not an issue from my position.

**Error is about playerHealth.currentHealth on the if statement. I also searched for answers and i someone suggested to Debug the playerHealth variable to see if it's null (playerHealth = player.GetComponent ();). And it's actually null. But i dont understand why

The code :

 using UnityEngine;
 using System.Collections;
 
 namespace CompleteProject
 {
     public class EnemyAttack : MonoBehaviour
     {
         public float timeBetweenAttacks = 0.5f;     // The time in seconds between each attack.
         public int attackDamage = 10;               // The amount of health taken away per attack.
 
 
         Animator anim;                              // Reference to the animator component.
         GameObject player;                          // Reference to the player GameObject.
         PlayerHealth playerHealth;                  // Reference to the player's health.
         EnemyHealth enemyHealth;                    // Reference to this enemy's health.
         bool playerInRange;                         // Whether player is within the trigger collider and can be attacked.
         float timer;                                // Timer for counting up to the next attack.
 
 
         void Awake ()
         {
             // Setting up the references.
             player = GameObject.FindGameObjectWithTag ("Player");
             playerHealth = player.GetComponent <PlayerHealth> ();
 
             if (playerHealth == null)
             {
                 Debug.LogError("Is Null"); // this code is execute. playerHealth is actually null
             }
 
             enemyHealth = GetComponent<EnemyHealth>();
             anim = GetComponent <Animator> ();
         }
 
 
         void OnTriggerEnter (Collider other)
         {
             // If the entering collider is the player...
             if(other.gameObject == player)
             {
                 // ... the player is in range.
                 playerInRange = true;
             }
         }
 
 
         void OnTriggerExit (Collider other)
         {
             // If the exiting collider is the player...
             if(other.gameObject == player)
             {
                 // ... the player is no longer in range.
                 playerInRange = false;
             }
         }
 
 
         void Update ()
         {
             // Add the time since Update was last called to the timer.
             timer += Time.deltaTime;
 
             // If the timer exceeds the time between attacks, the player is in range and this enemy is alive...
             if(timer >= timeBetweenAttacks && playerInRange && enemyHealth.currentHealth > 0)
             {
                 // ... attack.
                 Attack ();
             }
 
             // If the player has zero or less health...
             if(playerHealth.currentHealth <= 0) // object reference error here
             {
                 // ... tell the animator the player is dead.
                 anim.SetTrigger ("PlayerDead");
             }
         }
 
 
         void Attack ()
         {
             // Reset the timer.
             timer = 0f;
 
             // If the player has health to lose...
             if(playerHealth.currentHealth > 0) // object reference error here
             {
                 // ... damage the player.
                 playerHealth.TakeDamage (attackDamage);
             }
         }
     }
 }