Unity - Error: Object Reference not set to an instance of an Object - Instantiate

Question

I made the Survival Shooter tutorial that can be found in the Unity Asset store at https://www.assetstore.unity3d.com/en/#! /content/21028

The game is working, but is giving this following error in the code. How do I solve this?

NullReferenceException: Object reference not set to an instance of an object EnemyManager.Spawn () (at Assets/Scripts/Managers/EnemyManager.cs:26)
(Instantiate (enemy, spawnPoints[spawnPointIndex].position, spawnPoints[spawnPointIndex].rotation);)

this error appears just when the game starts and the dolls start attacking the player.

The code is as follows, which is the same as the tutorial for your channel and the Unity website:

using UnityEngine;

public class EnemyManager : MonoBehaviour
{
    public PlayerHealth playerHealth;       // Reference to the player's heatlh.
    public GameObject enemy;                // The enemy prefab to be spawned.
    public float spawnTime = 3f;            // How long between each spawn.
    public Transform[] spawnPoints;         // An array of the spawn points this enemy can spawn from.


    void Start ()
    {
        // Call the Spawn function after a delay of the spawnTime and then continue to call after the same amount of time.
        InvokeRepeating ("Spawn", spawnTime, spawnTime);
    }


    void Spawn ()
    {
        // If the player has no health left...
        if(playerHealth.currentHealth <= 0f)
        {
            // ... exit the function.
            return;
        }

        // Find a random index between zero and one less than the number of spawn points.
        int spawnPointIndex = Random.Range (0, spawnPoints.Length);

        // Create an instance of the enemy prefab at the randomly selected spawn point's position and rotation.
        Instantiate (enemy, spawnPoints[spawnPointIndex].position, spawnPoints[spawnPointIndex].rotation);
    }
}

Answer 1

Understanding the Problem

The mistake Object reference not set to an instance of an object happens when you work with some variable that has not been instantiated.

In Unity the method Instantiate can be used in two ways

1. Instantiate(original: Object);
2. Instantiate(original: Object, position: Vector3, rotation: Quaternion);

http://docs.unity3d.com/ScriptReference/Object.Instantiate.html

In your code you pass enemy and the spawnPoints

Instantiate (enemy, spawnPoints[spawnPointIndex].position, spawnPoints[spawnPointIndex].rotation);

And are created and instantiated in:

public GameObject enemy;                // The enemy prefab to be spawned.
public Transform[] spawnPoints;

You pass it as a parameter by Inspector of your object of play EnemyManager.

There should be something like that:

If one is missing it can happen this problem

Possible Solutions

I recommend you see two things:

1. if the Prefab of all characters exist (Zombunny, zombear and hellephant), they may have disappeared during the migration to Unity 5 that happened in recent weeks.

2. If all spawnPoints exist in your Unity’s Hierarchy as shown below.

If your images match mine it might work. Otherwise it is important that you share more information.

Add a screenshot of your elements to help with the investigation if that answer doesn’t help you.