how to make it work? !EventSystem.current.IsPointerOverGameObject()

I started with the book "unity in action" and got to the point of clicking on the gui with
````
using UnityEngine.EventSystems;
.....
void Update() { if (Input.GetMouseButtonDown(0) && !EventSystem.current.IsPointerOverGameObject())
.......
}
Without !EventSystem.current.IsPointerOverGameObject() everything works, but after an error comes out
```
NullReferenceException: Object reference not set to an instance of an object
RayShooter.Update () (at Assets/scripts/RayShooter.cs:27)
```
Maybe someone studied this book and found a solution to the problem? Veria unity 2019.4.
Thanks.

 

Did you add an EventSystem to your scene?

 

Yes, i have ' UnityEngine.EventSystems; '

 

No im not asking about a using statement in your code. There's an actual EventSystem component that needs to be attached to a GameObject in your scene. You can create it from the menu similar to how you would create a cube etc.