NullReferenceException when using gameObject.SetActive(false);

I have published my app on the ios app store last week.

I'm using unity 5 and using Game Performance service to track my app's bugs or errors.

One of the report confused me and I have no idea to fix it.

The report is :

And here is the code,CommonTooltipCarrayOverPanel is a MonoBehaviour:

  public void OnCloseBtnClick()
     {
         UnShow();
     }
 
 public void UnShow()
 {
     gameObject.SetActive(false);
 }

So , why the MonoBehavior is running it's code but the attached gameobject is null?