Unity C# Health/Damage Script works as intended but returns Object Reference error

Question

Does anyone know why im getting this error?

Object reference not set to an instance of an object HealthBar.TakeDamage (System.Int32 damage) (at Assets/Scripts/HealthBar.cs:61) HealthBar.Update () (at Assets/Scripts/HealthBar.cs:36)

the code seems to work as intended when i try to run "TakeDamage()" but i recieve that error after it executes even though its giving me the correct behavior.

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

public class HealthBar : MonoBehaviour
{
    public CharacterStats stats;
    public Slider slider;

    
    // Start is called before the first frame update
    void Start()
    {
        slider.value = slider.maxValue;
    }

    // Updates the Current Hp Text
    public Text valueText;

    public void OnSliderChanged(float value)
    {
        valueText.text = value.ToString();
    }

    // Update is called once per frame
    void Update()
    {
        if (Input.GetKeyDown(KeyCode.Space))
        {
            HealDamage(30);
            Debug.Log("Space");
        }
        if (Input.GetKeyDown(KeyCode.E))
        {
            TakeDamage(10);
            Debug.Log("E");
        }
        if (Input.GetKeyDown(KeyCode.Q))
        {
            TempMaxHealth(5f,20);
            Debug.Log("Q");
        }
        if (Input.GetKeyDown(KeyCode.T))
        {
            SetHealth(20);
            Debug.Log("T");
        }

        if (Input.GetKeyDown(KeyCode.P))
        {
            PoisonDamage(2f,10);
            Debug.Log("P");
        }
    }


    // Take X amount of Damage 
    void TakeDamage(int damage)
    {
        if (stats.Armor.GetValue() <= damage) { 
            damage -= stats.Armor.GetValue();
            damage = Mathf.Clamp(damage, 0, int.MaxValue);

            slider.value -= damage;
        }
        if (slider.value <= 0)
        {
            Dead();
        }
    }

    // Death Status
    void Dead()
    {
        Debug.Log("You Are Dead");
        //filler for death scene
    }

    // Heal X amount of Damage
    void HealDamage(int damage)
    {
        if (slider.value < slider.maxValue)
        {
            slider.value += damage;
        }
    }

    // Set Max Health Permanently
    public void SetMaxHealth(int health)
    {
        slider.maxValue = health;
    }

    // Set Current Health
    public void SetHealth(int health)
    {
        slider.value = health;
    }

    // Increase MaxHealthPermanently
    public void IncreaseMaxHealth(int health)
    {
        slider.maxValue = slider.maxValue + health;
    }

    // Temporarily increase Max Health. waitTime = 5f ~ 5 seconds
    public void TempMaxHealth(float waitTime,int health)
    {
        StartCoroutine(TempHealthTime(waitTime, health)); // start time function
    }

    IEnumerator TempHealthTime(float waitTime, int health) 
    {
        slider.maxValue += health; // adds boost
        yield return new WaitForSeconds(waitTime);
        Debug.Log("Coroutine ended: " + Time.time + " seconds");
        slider.maxValue -= health; // remove boost
    }

    public void PoisonDamage(float waitTime,int health)
    {
        StartCoroutine(PoisonDuration(waitTime, health));
    }

    IEnumerator PoisonDuration(float waitTime,int health)
    {
        
        slider.value -= health;
        if (slider.value <= 0)
        {
            slider.value = 1;
        }

        yield return new WaitForSeconds(waitTime);

        if (slider.value > 1)
        {
            PoisonDamage(waitTime, health);
        }
          else Debug.Log("Coroutine ended: " + Time.time + " seconds" + slider.value);
        
       
    }
}

Answer 1

This is because either stats or stats.Armor returns null. If that's excepted, you can do this

// Take X amount of Damage 
void TakeDamage(int damage)
{
    // note here the use of `?`, this basically says that if is null, use null and don't check after the dot.
    var armorValue = stats?.Armor?.GetValue();
    
    if (armorValue is null)
        return null;

    if (armorValue <= damage) { 
        damage -= armorValue;
        damage = Mathf.Clamp(damage, 0, int.MaxValue);

        slider.value -= damage;
    }
    if (slider.value <= 0)
    {
        Dead();
    }
}