Problem with Instantiate (maybe)

Hello Community, i've a problem with my code. In this code, a canon will shoot bullets.

 var LookAtTarget : Transform;
 var damping : float = 6.0;
 var bullet_Prefab : Transform;
 var savedTime = 0;
 function Update () {
     if (LookAtTarget){
         var rotate = Quaternion.LookRotation(LookAtTarget.position - transform.position);
         
         transform.rotation = Quaternion.Slerp(transform.rotation, rotate, Time.deltaTime * damping);
         
         var secounds : int = Time.time;
         var oddeven = (secounds % 2);
         
         if (oddeven){
             shoot();
         }
     }
 }
 
 function shoot(){
     if(secounds != savedTime){
         var bullet = Instantiate(bullet_Prefab, transform.Find("SpawnPoint").transform.position, Quaternion.indentity);
         
         bullet.rigidbody.AddForce(transform.forward * 1000);
         
         savedTime = secounds;
     }
 }

Million Errors occur ,when i start the game:

NullReferenceException: Object reference not set to an instance of an object TurnetController.shoot () (at Assets/Scripts/TurnetController.js:23) TurnetController.Update () (at Assets/Scripts/TurnetController.js:16)

I hope you can help me and sorry for my bad English.

Thank you in advance!