Object Reference Set To Null

I keep getting the error:
This is my health script:

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. using UnityEngine.UI;
5. public class Health : MonoBehaviour
6. {
7.     int health;
8.     int healthMax;
9.  
10.     public Image healthBar;
11.  
12.     public Health(int healthMax)
13.     {
14.         this.healthMax = healthMax;
15.         health = healthMax;
16.     }
17.  
18.     public int GetHealth()
19.     {
20.         return health;
21.     }
22.  
23.     public void Damage(int damageTaken)
24.     {
25.         health -= damageTaken;
26.         healthBar.fillAmount -= damageTaken/100f;
27.  
28.         if (health < 0)
29.         {
30.             health = 0;
31.         }
32.     }
33.  
34.     public void Heal(int healAmount)
35.     {
36.         health += healAmount;
37.         healthBar.fillAmount -= healAmount / 100f;
38.  
39.         if (health > healthMax)
40.         {
41.             health = healthMax;
42.         }
43.     }
44. }

 

You can't use constructors with MonoBehaviours. It's instanced when added to a GameObject via click-drag or by using

go.AddComponent<Health>()

.

 

Sorry, I am new, what should i do?

 

Never mind, I figured it out