Getting error "Object reference not set to an instance of an object"

Hello guys,

I am working on a game where my camera is moving right in x axis and I have some game objects which are going from right to left. I am instantiating those game objects so they are clones. Now I am deleting these clones when they move out of camera view by calling function KillClones. Function has the following.

(CameraControll.cordi gives me the current x co-ordinate of my moving camera).

 function KillClones(){
 
 if (GameObject.Find(Item1.name + "(Clone)").transform.position.x<CameraControll.cordi){
 Destroy(GameObject.Find(Item1.name + "(Clone)"));
 } 

It is working fine but in the console I am getting the following error

 NullReferenceException: Object reference not set to an instance of an object
 GameMaster.KillClones () (at Assets/Scripts/GameMaster.js:153)
 GameMaster.Update () (at Assets/Scripts/GameMaster.js:78)

How to remove this error, or should I use any other way to delete clones, please let me know

Thanks in advance