UNET NetworkBehaviour

 import UnityEngine.Networking;

 import UnityEngine.UI;
 
 public var hedef : Transform;
 
 private var canAttack : boolean;
 
 var hiz : float = 250;
 
 var Efekt : Rigidbody;
 
 var ses : AudioClip;
 
 var cooldown : float;
 
 var cooldowntime : float = 0;
 
 var rayhit : RaycastHit;

 public class TaretYapayZeka extends NetworkBehaviour {


 function FixedUpdate () {


         if(Physics.Raycast(transform.position, transform.TransformDirection(Vector3(0,0,1000)), rayhit, 1000) 
         &&
         rayhit.collider.gameObject.tag == "Player"
         &&
         cooldowntime<=0
         &&
         canAttack == true
         )
         {    
             CmdSaldiri();
 
         }
     }
 
     //Debug.DrawRay(transform.position, transform.TransformDirection(Vector3(0,0,1000)), Color.red);

@Command function CmdSaldiri (){

     RpcSaldiri();
 }

@ClientRpc function RpcSaldiri (){

     cooldowntime = cooldown;
     
     GetComponent.<AudioSource>().PlayOneShot(ses, 0.7);
         
     clone = Instantiate(Efekt, transform.position, transform.rotation);
         
     clone.velocity = transform.TransformDirection (Vector3.forward * hiz);
 }

}

when i try to shoot i get this error message: NullReferenceException: Object reference not set to an instance of an object UnityEngine.Networking.NetworkBehaviour.get_isServer () (at C:/buildslave/unity/build/Extensions/Networking/Runtime/NetworkBehaviour.cs:19) TaretYapayZeka.CallCmdSaldiri () TaretYapayZeka.FixedUpdate () (at Assets/Scriptler/TaretYapayZeka.js:74)