Health Bar NullReferenceException

I am trying to integrate a health bar system into my project. I have already got a script on my enemy that causes damage to my player on collision, and player health goes down correctly (which I can see via Debug.Log). However, for some unknown reason the Health Bar transforms straight to 0, and the text shows 0% after just one hit from the enemy. Any help would be much appreciated.

Code for HealthBar:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 
 public class PlayerUI : MonoBehaviour {
 
     public static int playerCurrentHealth;
     public Text gameOverText;
     public Image currentHealth; //Healthbar
     public Text healthPercentText; //Healthbar
 
     void Awake ()
     {
         playerCurrentHealth = gameObject.GetComponent<PlayerStats> ().playerMaxHealth;
     }
 
     private void Start()
     {
         UpdateHealthBar ();
     }
 
     public void UpdateHealthBar()
     {
         int healthPercent = playerCurrentHealth / (gameObject.GetComponent<PlayerStats> ().playerMaxHealth); 
         currentHealth.rectTransform.localScale = new Vector3 (healthPercent, 1, 1); //Needs fixing, health bar doesn't change!
         healthPercentText.text = (healthPercent * 100).ToString () + '%'; //Displays 100% but doesn't update!
     }
 }

Code for Enemy Damage:

     void OnCollisionStay(Collision attack) //Attacking the player
     {
         if (attack.gameObject.tag == "Player" && PlayerUI.playerCurrentHealth > 0 && Time.time > enemyAttackTimer) 
         {
             PlayerUI.playerCurrentHealth -= (gameObject.GetComponent<EnemyStats>().enemyDamage - GameObject.Find ("Player").GetComponent<PlayerStats> ().playerArmorRating);
             GameObject.Find ("Player").GetComponent<PlayerUI> ().UpdateHealthBar (); //This line is to call health bar function UpdateHealthBar
             Debug.Log ("You have been hit! Current Health: " + PlayerUI.playerCurrentHealth);
             enemyAttackTimer = Time.time + gameObject.GetComponent<EnemyStats> ().enemyAttackDelay;
         }
     }

EDIT: I had NullReferenceExceptions appearing on play, but had 2 of the same script attached to the player and one missing object references. Problem of health dropping straight to zero still persists.