Argument Null Exception

[Sinum]

Hello again, I am having a lot of questions today, so here is my next issue:
the following error:
ArgumentNullException: Value cannot be null.
Parameter name: key
System.Collections.Generic.Dictionary2[TKey,TValue].FindEntry (TKey key) (at <51ee0c51c90047b488b10b1b78b365d8>:0) System.Collections.Generic.Dictionary2[TKey,TValue].ContainsKey (TKey key) (at <51ee0c51c90047b488b10b1b78b365d8>:0)
RPG.InventorySystem.InventoryItem.GetFromID (System.String itemID) (at Assets/MyAssets/Scripts/Inventories/InventoryItem.cs:54)
RPG.InventorySystem.Inventory.RPG.Saving.ISaveable.RestoreState (System.Object state) (at Assets/MyAssets/Scripts/Inventories/Inventory.cs:221)
RPG.Saving.SaveableEntity.RestoreState (System.Object state) (at Assets/MyAssets/Scripts/Saving/SaveableEntity.cs:35)
RPG.Saving.SavingSystem.RestoreState (System.Collections.Generic.Dictionary`2[TKey,TValue] state) (at Assets/MyAssets/Scripts/Saving/SavingSystem.cs:77)
RPG.Saving.SavingSystem+d__0.MoveNext () (at Assets/MyAssets/Scripts/Saving/SavingSystem.cs:24)
UnityEngine.SetupCoroutine.InvokeMoveNext (System.Collections.IEnumerator enumerator, System.IntPtr returnValueAddress) (at <579f6a25593149bdb5b2b685692d23ea>:0)

and it appears to point to the following code:

        public static InventoryItem GetFromID(string itemID)
        {
            if (itemLookupCache == null)
            {
                itemLookupCache = new Dictionary<string, InventoryItem>();
                var itemList = Resources.LoadAll<InventoryItem>("");
                foreach (var item in itemList)
                {
                    if (itemLookupCache.ContainsKey(item.itemID))
                    {
                        Debug.LogError(string.Format("Looks like there's a duplicate GameDevTV.UI.InventorySystem ID for objects: {0} and {1}", itemLookupCache[item.itemID], item));
                        continue;
                    }

                    itemLookupCache[item.itemID] = item;
                }
            }

            if (itemID == null || !itemLookupCache.ContainsKey(itemID)) return null;
            return itemLookupCache[itemID];
        }
        /// <summary>

As well as:

        {
            var slotRecords = (InventorySlotRecord[])state;
            for (int i = 0; i < inventorySize; i++)
            {
                slots[i].item = InventoryItem.GetFromID(slotRecords[i].itemID);
                slots[i].number = slotRecords[i].number;
            }
            if (inventoryUpdated != null)
            {
                inventoryUpdated();
            }
        }

Thank you once again in advance!

[Sinum]

Update: This was fixed by naming the weapons and replacing their ID’s. Why? No clue, but it worked!

[Brian_Trotter]

Usually this is because the ItemID hasn’t been properly initialized on the InventoryItem. So when CaptureState returns the InventoryItem’s InventoryID, it saves a null string, which… completely breaks a Dictionary that requires that any object used as an indexer into the Dictionary cannot be null.