MoveAround Failed Fire Ball

İm code Error. Please Help Me.(UnassignedReferenceException: The variable bullitPrefab of 'MoveAround' has not been assigned. You probably need to assign the bullitPrefab variable of the MoveAround script in the inspector.)

 var speed : float = 3.0; 
 var rotateSpeed : float = 3.0; 
 var bullitPrefab:Transform;
 
 function Update () 
 { 
     var controller : CharacterController = GetComponent(CharacterController);
     
     transform.Rotate(0, Input.GetAxis ("Horizontal") * rotateSpeed, 0);
     
     var forward : Vector3 = transform.TransformDirection(Vector3.forward);
     var curSpeed : float = 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 * 200);
     }
 } 
 
 @script RequireComponent(CharacterController)