Error NullReferenceException

Hello sorry I am new to unity and having trouble instantiating a camera on button down and turning my main off then having the "newCamera" follow my "newAmmo" projectile until its destroyed or the "cameraChange" goes up Here is the code I tried again sorry I am new and don't know all the posting rules either

#pragma strict

static var canThrow : boolean = true;
var throwSound : AudioClip;
var ammoObject : Rigidbody;
var throwForce : float;
var arc : float;
private var changeCamera : boolean;
var ammoCamera : Camera;
function Start ()
{


}

function Update ()
{

if(Input.GetButtonUp("Fire1") canThrow)
{
//Script for creating Ammo projectile on mouse click down
//Works good
audio.PlayOneShot(throwSound);
var newAmmo : Rigidbody = Instantiate(ammoObject,transform.position, transform.rotation);
newAmmo.name = "Ammo";



newAmmo.transform.Rotate(0,90,-5);
newAmmo.rigidbody.velocity = transform.TransformDirection(Vector3(0,0, throwForce));
Physics.IgnoreCollision(transform.root.collider,newAmmo.collider, true);

}
// Change camera to Ammo only on true conditions
// changeCamera "F" button down and Ammo object is instantiated
if(Input.GetButtonDown("changeCamera") GameObject.Find("Ammo") != null)
{
var newCamera = Instantiate(ammoCamera,transform.position, transform.rotation);
newCamera.name ="ammoCamera";

Camera.main.enabled = false;
newCamera.enabled= true;


newCamera.transform.parent = newAmmo.transform;

}

// Change Camera Back only on true conditions
// changeCamera "F" button up and Ammo object is instantiated
if(Input.GetButtonUp("changeCamera") GameObject.Find("Ammo") != null)
{
newCamera.enabled= false;
Camera.main.enabled = true;
}


}
@script RequireComponent(AudioSource)

I get an error only when changeCamrea button is pressed and the error is on line
newCamera.transform.parent = newAmmo.transform;

I have a camera prefab named ammoCamera dragged and loaded I also see the ammoCamera being created in the hiearchy but still get a null reference exception I am lost again sorry I am new and don't know all the rules

 

http://forum.unity3d.com/threads/143875-Using-code-tags-properly

--Eric