Turret AI problem

Unity Engine
1

I’m having another problem!

Error:

NullReferenceException
TurretAI.Shoot (System.Object seconds) (at Assets/Game/BasicGameMechanics/TurretAI/TurretAI.js:32)
TurretAI.Update () (at Assets/Game/BasicGameMechanics/TurretAI/TurretAI.js:19)

Code:

var LookAtTarget:Transform;
var damp = 2.0;
var bulletPrefab: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 * damp);
        
        var seconds : int = Time.time;
        var oddeven = (seconds % 2);
        
        if(oddeven)
        {
            Shoot(seconds);
        }
    }
}

function Shoot(seconds)

{

    if(seconds!=savedTime)

    {

        var bullet = Instantiate(bulletPrefab ,transform.Find("Sphere").transform.position ,Quaternion.identity) as GameObject;

 

        bullet.rigidbody.AddForce(transform.forward * 1500);

 

        savedTime=seconds;

     }

}
2 
        var bullet = Instantiate(bulletPrefab ,transform.Find("Sphere").transform.position ,Quaternion.identity) as GameObject;

Bulletprefab is null. Be sure to set it in the inspector.