Null Reference

Questions & Answers
1

These scripts were working earlier but now it says that there is a null refference.

NullReferenceException: Object reference not set to an instance of an object
PlayerHealth.AddHealth (Int32 amount) (at Assets/Scripts/Player/PlayerHealth.cs:56)
PlayerAddHealth.OnTriggerEnter (UnityEngine.Collider player) (at Assets/Scripts/Player/PlayerAddHealth.cs:24)

using UnityEngine;
using System.Collections;

public class PlayerAddHealth : MonoBehaviour
{
	public int addHealth = 10;
	public int startingHealth = 100;
	public int currentHealth;

	public GameObject player;
	public PlayerHealth playerHealth;
	
	void Awake ()
	{
		player = GameObject.FindGameObjectWithTag ("Player");
		playerHealth = player.GetComponent<PlayerHealth> ();
	}

	void OnTriggerEnter (Collider player)
	{
		if (playerHealth.currentHealth > 0)
		{
			playerHealth.AddHealth (addHealth);
		}
	}
}
using UnityEngine;
using UnityEngine.UI;
using System.Collections;

I dont really see the problem in any of these but I’m wrong so help would be appreciated.

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

public class PlayerHealth : MonoBehaviour
{
    public int startingHealth = 100;
    public int currentHealth;
	public int maxHealth = 100;
    public Slider HealthSlider;
    public Image damageImage;
    public AudioClip deathClip;
    public float flashSpeed = 5f;
    public Color flashColour = new Color(1f, 0f, 0f, 0.1f);

	Animator anim;
    AudioSource playerAudio;
    PlayerMovement playerMovement;
    PlayerShooting playerShooting;
    bool isDead;
    bool damaged;


    void Awake ()
    {
        anim = GetComponent <Animator> ();
        playerAudio = GetComponent <AudioSource> ();
        playerMovement = GetComponent <PlayerMovement> ();
        playerShooting = GetComponentInChildren <PlayerShooting> ();
        currentHealth = startingHealth;
    }

	void Start ()
	{
		currentHealth = maxHealth;
	}

     void Update ()
    {
        if(damaged)
        {
            damageImage.color = flashColour;
        }
        
		else
        {
            damageImage.color = Color.Lerp (damageImage.color, Color.clear, flashSpeed * Time.deltaTime);
        }
        damaged = false;
    }

	public void AddHealth (int amount)
	{
		currentHealth += amount;

		HealthSlider.value = currentHealth;

		if (currentHealth <= 0) 
		{
			currentHealth = 0;
		}
		
		if (currentHealth >= maxHealth)
		{
			currentHealth = maxHealth;
		}
	}

	public void TakeDamage (int amount)
    {
        damaged = true;

        currentHealth -= amount;

		HealthSlider.value = currentHealth;

        playerAudio.Play ();
		
		if (currentHealth <= 0 && !isDead)
		{
			Death ();
		}
    }
	
    public void Death ()
    {
        isDead = true;

        playerShooting.DisableEffects ();

        anim.SetTrigger ("Die");

        playerAudio.clip = deathClip;
        playerAudio.Play ();

        playerMovement.enabled = false;
        playerShooting.enabled = false;
    }

	public void RestartLevel ()
    {
        Application.LoadLevel (Application.loadedLevel);
    }
}
2

Basically “HealthSlider is null. In PlayerHealth, line 56”

Is "HealthSlider " null/empty in the inspector for PlayerHealth?