Question Calling properties from other Script instances

I have set up two cubes as children on my Character Controller to act as extra collision detectors. I don't think I'm creating instances properly? Both cubes have scripts on them, I need to access those properties from Character Controller script.

Console error in Unity:
NullReferenceException: Object reference not set to an instance of an object
CapsuleController.checkCollision () (at Assets/Scripts/CharacterController.cs:56)
CapsuleController.Update () (at Assets/Scripts/CharacterController.cs:50)

On the main CharacterController script:
(Edit: code updates as I try to fix this)

Code (CSharp):

1.     public class UpperCollisionScript : MonoBehaviour
2.     {
3.         public GameObject upperCollisionObject; //linked to objects in Unity Inspector
4.         public GameObject lowerCollisionObject;
5.    
6.         void Update()
7.         {
8.             checkCollision();
9.         }
10.    
11.         private void checkCollision()
12.         {
13.             Debug.Log("checkCollision() called"); //is called
14.             int uLayer = lowerCollisionObject.GetComponent<UpperCollisionScript>().ULayer;
15.             int lLayer = upperCollisionObject.GetComponent<LowerCollisionScript>().LLayer;
16.             Debug.Log(uLayer); //nothing logged
17.             Debug.Log(lLayer); //nothing logged
18.  
19.             if (uLayer == 9 && lLayer == 9) //checking layers the two objects collide with and changing player status
20.             {
21.                 status = MovementStatus.scale;
22.             }
23.             else if (uLayer == 9 && lLayer == 8)
24.             {
25.                 status = MovementStatus.normal;
26.             }
27.             else if (uLayer == 9 && lLayer != 9)
28.             {
29.                 status = MovementStatus.scale;
30.             }
31.         }
32.    
33.     }
34. }

And the scripts on the two objects are like so:

Code (CSharp):

1. public class UpperCollisionScript : MonoBehaviour
2. {
3.  
4.     private int uLayer = 8; //groundLayer
5.  
6.     public int ULayer
7.     {
8.         get => uLayer;
9.         set => uLayer = value;
10.     }
11.  
12.     private void OnCollisionEnter(Collision other)
13.     {
14.         Debug.Log("upper collision occurred"); //does not get called on collision
15.         uLayer = other.gameObject.layer;
16.     }
17.  
18.     private void OnCollisionExit(Collision other)
19.     {
20.         uLayer = 8; //groundLayer
21.     }
22. }

The upper and lower collision scripts are on the components, the component is called within the script in Awake() so I don't know why OnCollisionEnter is not executed and debugs are not showing in console.

 

has all the answers I need.