Infinite Items in the Inventory

Question

I've been following this tutorial series: https://www.youtube.com/watch?v=LcizwQ7ogGA&list=PLJWSdH2kAe_Ij7d7ZFR2NIW8QCJE74CyT&index=3 I'm on part 3 of 10.

Good series so far, however I've hit a very major problem. When I go over to pick an item up, it recreates the item, indefinately causing the enitre game to lag very quickly, Figure 1. I'm not sure what else to do as anything I do doesn't fix it at all. Is there anything anytone can spot that is wrong or that is causing this? The only error I get is that Line 48's object reference is not set to an instance of an object, Figure 2. This might be because I have a new prefab in the Inspector, Figure 3.

Here is the code for Display Inventory:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;

public class DisplayInventory : MonoBehaviour
{
    public GameObject inventoryPrefab;

    public InventoryObject inventory;

    public int xStart;
    public int yStart;

    public int xSpaceBetweenItem;
    public int numberOfColumns;
    public int ySpaceBetweenItem;

    Dictionary<InventorySlot, GameObject> itemsDisplayed = new Dictionary<InventorySlot, GameObject>();

    // Start is called before the first frame update
    void Start()
    {
        CreateDisplay();
    }

    // Update is called once per frame
    void Update()
    {
        UpdateDisplay();
    }

    public void UpdateDisplay()
    {
        for (int i = 0; i < inventory.Container.Items.Count; i++)
        {
            InventorySlot slot = inventory.Container.Items[i];

            if (itemsDisplayed.ContainsKey(slot))
            {
                itemsDisplayed[slot].GetComponentInChildren<Text>().text = inventory.Container.Items[i].amount.ToString("n0");
            }
            else
            {
                var obj = Instantiate(inventoryPrefab, Vector3.zero, Quaternion.identity, transform);
                obj.transform.GetChild(0).GetComponentInChildren<Image>().sprite = inventory.database.GetItem[slot.item.id].uiDisplay;
                obj.GetComponent<RectTransform>().localPosition = GetPosition(i);
                obj.GetComponentInChildren<Text>().text = slot.amount.ToString("n0");
                itemsDisplayed.Add(inventory.Container.Items[i], obj);
            }
        }
    }

    public void CreateDisplay()
    {
        for (int i = 0; i < inventory.Container.Items.Count; i++)
        {
            InventorySlot slot = inventory.Container.Items[i];

            var obj = Instantiate(inventoryPrefab, Vector3.zero, Quaternion.identity, transform);
            obj.transform.GetChild(0).GetComponentInChildren<Image>().sprite = inventory.database.GetItem[slot.item.id].uiDisplay;
            obj.GetComponent<RectTransform>().localPosition = GetPosition(i);
            obj.GetComponentInChildren<Text>().text = slot.amount.ToString("n0");
            itemsDisplayed.Add(slot, obj);
        }
    }

    public Vector3 GetPosition(int i)
    {
        return new Vector3(xStart + (xSpaceBetweenItem * (i % numberOfColumns)), yStart + (-ySpaceBetweenItem * (i / numberOfColumns)), 0f);
    }
}