NullReference Exception when adding a class

Questions & Answers
1

Hello everyone. I’m developing a shooting game with different types of bullets (pressing 1, 2, 3 and 4 will change them). I have a BasicBullet.cs which is like this

using UnityEngine;
using System.Collections;

public class BasicBullet : MonoBehaviour
{
	public float speed = 5.0f;
	public float DestroyTime = 10.0f;
	public Vector3 velocity;
	
	public void changeVelocity(Vector3 v)
	{
		velocity = v;
	}

	void Start ()
	{
		Destroy (gameObject, DestroyTime);
	}


	void FixedUpdate ()
	{
		// TO DO
		transform.position += velocity * Time.deltaTime;
	}
	
}

And my second bullet is like this
using UnityEngine;
using System.Collections;

public class Bullet2 : MonoBehaviour {

	public float speed = 5.0f;
	public float DestroyTime = 10.0f;
	public Vector3 velocity;
	
	public void changeVelocity(Vector3 v)
	{
		velocity = v;
	}
	
	void Start ()
	{
		Destroy (gameObject, DestroyTime);
	}
	
	
	void FixedUpdate ()
	{
		// TO DO
		transform.position += velocity * Time.deltaTime;
	}
}

which basically are the same, just for tests purposes.
Now, in my player shooting part, this is the code that I have

using UnityEngine;
using System.Collections;

public class Shoot : MonoBehaviour
{
	public AudioClip shootAudio;
	private AudioSource audioSource;
	public GameObject bulletPrefab;
	public GameObject fireParticle;
	public float fireRate = 0.1f;
	
	private float nextFire = 0.0f;
	private bool shooting = false;
	private int gunMode = 1;
	
	void Start()
	{
		audioSource = GetComponent<AudioSource>();
		
	}

	// Update is called once per frame
	void Update ()
	{
		//use mouse to fire
		if (Input.GetButtonDown ("Fire1"))
			shooting = true;
		if (Input.GetButtonUp ("Fire1"))
			shooting = false;
		
		//use keyboard to change gun type
		if (Input.GetKey("1"))
			gunMode = 1;
		else if(Input.GetKey("2"))
			gunMode = 2;
		else if(Input.GetKey("3"))
			gunMode = 3;
		else if(Input.GetKey("4"))
			gunMode = 4;
		
		if (shooting)
		{
			if(gunMode == 1  && Time.time > nextFire)
			{
				fireParticle.SetActive(false);
				audioSource.PlayOneShot(shootAudio);
				GameObject bullet = (GameObject)Instantiate(bulletPrefab,this.transform.position + this.transform.forward + this.transform.up, Quaternion.identity);
				
				BasicBullet bulletComp = bullet.GetComponent<BasicBullet>();
				bulletComp.changeVelocity(this.transform.forward * 10f);
				nextFire = Time.time + fireRate;
			}
			else if(gunMode == 2)
			{
				fireParticle.SetActive(true);
			}
			//TO DO
			else if(gunMode == 3 && Time.time > nextFire)
			{
				fireParticle.SetActive(false);
				audioSource.PlayOneShot(shootAudio);
				GameObject bullet = (GameObject)Instantiate(bulletPrefab,this.transform.position + this.transform.forward + this.transform.up, Quaternion.identity);
				
				Bullet2 bulletComp = bullet.GetComponent<Bullet2>(); //<----PROBLEM!!!
				bulletComp.changeVelocity(this.transform.forward * 10f);
				nextFire = Time.time + fireRate;
			}
			else if(gunMode == 4)
			{
				
			}
		}
		else
		{
			if(gunMode == 2)
			{
				fireParticle.SetActive(false);
			}
		}
	}
	
	void OnTriggerStay(Collider other)
	{
		//for Flamethrower
		if(gunMode == 2)
		{
			if (other.attachedRigidbody)
        	other.attachedRigidbody.AddForce(this.transform.forward * 50f);
		}
    }
}

but I get a NullReferenceException in here

Bullet2 bulletComp = bullet.GetComponent<Bullet2>();
				bulletComp.changeVelocity(this.transform.forward * 10f);
				nextFire = Time.time + fireRate;

What is the problem? Can anyone help me? Thanks!
The error is this one:

NullReferenceException: Object reference not set to an instance of an object
Shoot.Update () (at Assets/Scripts/Player/Shoot.cs:65)
2

You are instantiating the same prefab (bulletPrefab) in both cases. Is that intended behavior? If the prefab does not contain a Bullet2 script, GetComponent will return null, and you will get a NullReferenceException.

3

It looks like you’re trying to create a bullet object, but grabbing a component script. Bad form. First, generate a GameObject called BulletA, and attach Bullet1 to it. Next, generate a GameObject called BulletB, and attach Bullet2 to it. Drag them to your prefabs folder and delete it from your scene. Next, add a public GameObject bullet; to your Shoot script. This will allow you to drag-and-drop your BulletA or BulletB prefab as the designated item. In the case you want to spawn both bullets, create 2 public GameObject bullet_a, bullet_b; handles. Now, when you’ve decided this object should spawn, do something like this:

GameObject bullet = (GameObject) GameObject.Instantiate(bullet_a, transform.position, transform.forward);

That’s a temporary handle to a freshly spawned copy of bullet_a summoned at the parent scripts position, pointing forward in the parents direction.

From here, you can either throw the bullet by initial velocity, or raycast-teleport inside the Bullet1 script. Remember to destroy the bullet (preferably within it’s script) when it is deemed obsolete (out of game bound, collided, traveled for X seconds or meters).

This guy will get you going with tutorials and visual aids: ETeeskiTutorials(Youtube)