Question Object Reference not set to an instance of an Object error

I've checked other threads but they aren't helping, and my code seems to be fine.
It says it finds an error on line 20 of my mouse movement script.
This is my mousemovement script

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class MouseMovement : MonoBehaviour
6. {
7.     public float mouseSensitivity = 100f;
8.     float xRotation = 0f;
9.     float YRotation = 0f;
10.     void Start()
11.     {
12.       //Locking the cursor to the middle of the screen and making it invisible
13.       Cursor.lockState = CursorLockMode.Locked;
14.     }
15.     void Update()
16.     {
17.         if (InventorySystem.Instance.isOpen == false)
18.         {
19.        float mouseX = Input.GetAxis("Mouse X") * mouseSensitivity * Time.deltaTime;
20.        float mouseY = Input.GetAxis("Mouse Y") * mouseSensitivity * Time.deltaTime;
21.      
22.        //control rotation around x axis (Look up and down)
23.        xRotation -= mouseY;
24.        //we clamp the rotation so we cant Over-rotate (like in real life)
25.        xRotation = Mathf.Clamp(xRotation, -90f, 90f);
26.        //control rotation around y axis (Look up and down)
27.        YRotation += mouseX;
28.        //applying both rotations
29.        transform.localRotation = Quaternion.Euler(xRotation, YRotation, 0f);
30.        }
31.     }
32. }
33.  

and this is my inventory system script

Code (CSharp):

1. using System;
2. using System.Collections;
3. using System.Collections.Generic;
4. using UnityEngine;
5. public class InventorySystem : MonoBehaviour
6. {
7.    public static InventorySystem Instance { get; set; }
8.     public bool isOpen;
9.     public GameObject inventoryScreenUI;
10.     public List<GameObject> slotList = new List<GameObject>();
11.     public List<string> itemList = new List<string>();
12.     private GameObject itemToAdd;
13.     private GameObject whatSlotToEquip;
14.     public bool isFull;
15.  
16.     void Start()
17.     {
18.         isOpen = false;
19.         PopulateSlotList();
20.     }
21.     private void PopulateSlotList()
22.     {
23.         foreach (Transform child in inventoryScreenUI.transform)
24.         {
25.             if (child.CompareTag("Slot"))
26.             {
27.                 slotList.Add(child.gameObject);
28.             }
29.  
30.         }
31.     }
32.     void Update()
33.     {
34.         if (Input.GetKeyDown(KeyCode.I) && !isOpen)
35.         {
36.             Debug.Log("i is pressed");
37.             inventoryScreenUI.SetActive(true);
38.             Cursor.lockState = CursorLockMode.None;
39.             isOpen = true;
40.  
41.         }
42.         else if (Input.GetKeyDown(KeyCode.I) && isOpen)
43.         {
44.             inventoryScreenUI.SetActive(false);
45.             Cursor.lockState = CursorLockMode.Locked;
46.             isOpen = false;
47.         }
48.     }
49. }
50.  

If someone could help me debug this that would be great.

 

My guess is that your inventory system instance is null.

Code (CSharp):

1. InventorySystem.Instance

Where do you assign it? Maybe you need to do it in the Awake method of your InventorySystem script.

 

It's always the same answer, ALWAYS.

How to fix a NullReferenceException error

https://forum.unity.com/threads/how-to-fix-a-nullreferenceexception-error.1230297/

Three steps to success:
- Identify what is null <-- any other action taken before this step is WASTED TIME
- Identify why it is null
- Fix that

 

I already checked if it was null, and the same error occurred, because isOpen is a boolean and cannot be null.

 

You're right, it can't be.

Therefore you haven't actually completed Step #1 and yet you think you have.

The null object will be on the LEFT side of any dot (

.

) operator.

The computer says, "Your move."