Bullet Prefab Null reference?

I am trying to make a first person shooting game which my character shoots my bullet Prefab, however, it can't shoot out anything when I press space bar and unity said it was a null reference Exception error. I don't know what to do as a newbie and here below is my code and what should I do?

 function Update ()
  { 
 
 var controller : CharacterController = GetComponent(CharacterController);
 
 // rotate around y - axis 
 
       transform.Rotate(0, Input.GetAxis("Horizontal") * rotateSpeed, 0);
       
 // Move forward / backward
   var forward = transform.TransformDirection(Vector3.forward);
   var curSpeed = speed * Input.GetAxis("Vertical");
   controller.SimpleMove(forward * curSpeed);
   if(Input.GetButtonDown("Jump"))
   {
   var bullit = Instantiate(bullitPrefab, GameObject.Find("spawnPoint").transform.position, Quaternion.identity);
   bullit.rigidbody.AddForce(transform.forward *2000); 
   }
   }