Need help with error.

I did watch superroblox tutorials and did do same things as he did in in second tutorial.
Heres my script:
var Bullet : Rigidbody;
var Spawn : Transform;

function Start () {

}

function Update () {
    if(Input.GetButtonDown("Fire1")){
	    Fire();
}
}

function Fire(){
    var bullet1 = Instantiate(Bullet,Spawn.position,Spawn.Rotation);

}

And i got this error: NullReferenceException: Object reference not set to an instance of an object
Gun.Fire () (at Assets/Scripts/Gun.js:18)
Gun.Update () (at Assets/Scripts/Gun.js:13)
18 line:
var bullet1 = Instantiate(Bullet,Spawn.position,Spawn.Rotation);
13 line: Fire();
Sorry, but i’m first time at Unity.
I did Create empty for bullet spawn etc…

Without testing your code, did you attach an object to the variable ‘Bullet’ in the editor?, sounds like you didn’t.

Also should Spawn.Rotation be Spawn.rotation ?

Cheers