Shoot Script not working correctly

I was following this tutorial for a shoot script : LINK. I copied the script and I am having two errors. The first error is that the BulletsLeft doesnt go down when I shoot. The second error says:

NullReferenceException: Object reference not set to an instance of an object Shoot.Shot () (at Assets/Scripts/Shoot.js:71) Shoot.Update () (at Assets/Scripts/Shoot.js:47)

Line 71 is Debug.DrawRay(transform.posistion , DirectionRay * Range , Color.red);

Here is my Code

 var Range : float = 1000;
 var Force : float = 1000;
 var Clips : int = 2;
 var BulletsPerClip : int = 16;
 var ReloadTimer : float = 0;
 var ReloadCooler : float = 3.3;
 var Damage : int = 10;
 var BulletsLeft : int = 16;
 var ShootTimer : float = 0;
 var ShootCooler : float = 0.09;
 public var ShootSound : AudioClip;
 public var ReloadSound : AudioClip;
 public var EmptySound : AudioClip;
 var HitParticles : ParticleEmitter;
 function Start () 
 {
     BulletsLeft = BulletsPerClip;
     HitParticles.emit = false;
 }
 
 function Update ()
 {
     if(ReloadTimer > 0){
         ReloadTimer -= Time.deltaTime;
     }
     if(ReloadTimer < 0){
         ReloadTimer = 0;
     }
     
     if(ShootTimer > 0){
         ShootTimer -= Time.deltaTime;
     }
     if(ShootTimer < 0){
         ShootTimer = 0;
     }
     if(BulletsLeft < 0){
         BulletsLeft = 0;
     }
     if(Input.GetMouseButtonDown(0) && ShootTimer == 0)
     {
         if(BulletsLeft > 0)
         {
             if(ShootTimer == 0)
             {
                 PlayShootSound();
                 ShootTimer = ShootCooler;
                 Shot();
                 BulletsLeft --;
                 }
             }
             if(BulletsLeft == 0 && Clips == 0)
             {
                 if(ShootTimer == 0)
                 {
                     PlayEmptySound();
                     ShootTimer = ShootCooler;
                 }
             }
             if( BulletsLeft == 0 && Clips > 0 && ReloadTimer == 0)
             {
                 PlayReloadSound();
                 Reload();
             }
         }
     }
 function Shot ()
 {
 
     var Hit : RaycastHit;
     var DirectionRay = transform.TransformDirection(Vector3.forward);
     Debug.DrawRay(transform.posistion , DirectionRay * Range , Color.red);
     if(Physics.Raycast(transform.posistion , DirectionRay , Hit , Range))
     {
         if(Hit.rigidbody)
         {
             if(HitParticles)
             {
                 HitParticles.transform.posistion = Hit.point;
                 HitParticles.transform.localRotation = Quaternion.FromToRotation(Vector3.forward, Hit.normal);
                 HitParticles.Emit ();
                 Hit.rigidbody.AddForceAtPosition(DirectionRay * Force , Hit.point);
                 Hit.collider.SendMessageUpwards ("ApplyDamage" , Damage, SendMessageOptions.DontRequireReciever);
                 }
             }
         }
     }
 function Reload()
 {
     ReloadTimer = ReloadCooler;
     yield WaitForSeconds(ReloadTimer);
     BulletsLeft = BulletsPerClip;
     Clips -=1;
 }
 function PlayShootSound ()
 {
     audio.PlayOneShot (ShootSound);
 }
 function PlayReloadSound ()
 {
     audio.PlayOneShot (ReloadSound);
 }
 function PlayEmptySound ()
 {
     audio.PlayOneShot (EmptySound);
 }