Help with EventSystem IsPointerOverGameObject

I'm using Unity 2017.1.0f3 and I'm trying to block ui touches in a UI canvas from moving through to the game objects and came across the boredmormongames tutorial but am having trouble with the first example.

When I add the below code as a monobehaviour to the cubes in my scene I get the error:

NullReferenceException: Object reference not set to an instance of an object
MouseDetection.OnMouseUp () (at Assets/MouseDetection.cs:9)
UnityEngine.SendMouseEventsoSendMouseEvents(Int32)

I've researched and don't see an explanation.

Also, is there an equivalent to isPointerOverGameObject for mobile or will this work with both mouse and mobile touch? Thank you.

Code (CSharp):

1. using System.Collections;
2. using UnityEngine;
3. using UnityEngine.EventSystems;
4.  
5. public class MouseDetection : MonoBehaviour {
6.  
7.     bool isRed;
8.     public void OnMouseUp(){
9.         if(!EventSystem.current.IsPointerOverGameObject ()){
10.             isRed =! isRed;
11.             if(isRed){
12.                 GetComponent<Renderer>().material.color=Color.red;
13.             }
14.             else{
15.                 GetComponent<Renderer>().material.color=Color.white;
16.  
17.             }
18.         }
19.     }
20. }
21.  

 

do you have EventSystem in your scene hierarchy?

 

That was it. Thank you.