Scripts working in Editor, but not in build

Everything works great in the editor, but as soon as I try it in the build, some of the controls don't work, such as the Jump mechanic using the spacebar. It also gives me the following error: "NullReferenceException: Object reference not set to an instance of an object Player.Update () (at Assets/Scripts/Player/Player.cs:44)". Please help me! This project is due in less than a week!!

Here's the script that tracks the player's health and what not:

 {
     public Collision2D collision;
 
     GameObject playerObject;
     Collider2D player;
     Rigidbody2D player_rb;
     readonly AudioSource gg_player;
     
     [Header("Enemy Hook Config")]
     public Rigidbody2D nearestEnemy;
     public Transform nearestEnemyTransform;
 
     [Header("Health Tracking")]
     public HealthBar healthBar;
     public Slider healthSlider;
     public int maxHealth = 100;
     public int currentHealth;
 
     private void Start()
     {
         healthSlider = GetComponent<Slider>();
 
         // Get the nearest enemy transform and collider
         nearestEnemyTransform = FindObjectOfType<EnemyAI>().GetComponent<Transform>();
         nearestEnemy = GetComponent<Rigidbody2D>();
 
         // Set player health data
         healthBar.SetMaxHealth(maxHealth);
         healthBar.SetHealth(currentHealth);
         currentHealth = maxHealth;
     }
 
     void Update()
     {
         if (collision.gameObject.CompareTag("Enemy"))
         {
             TakeDamage(10);
         }
 
         if (currentHealth <= 0)
         {
             KillPlayer();
         }
         else
         {
             return;
         }
     }
 
     void KillPlayer()
     {
         SceneManager.LoadScene("GameOver");
     }
 
     //public void OnCollisionEnter2D()
     //{
     //    if(collision.collider.gameObject.CompareTag("Enemy"))
     //    {
     //        TakeDamage(10);
     //    }
     //}
 
     void TakeDamage(int damage)
     {
         currentHealth -= damage;
         healthBar.SetHealth(currentHealth);
     }
 }