Editor.CreateEditor returns null for an object type with a custom editor

So I'm working on a custom editor for an object that essentially stores a list of other objects. The idea is to make a bunch of foldouts (dropdowns) in the inspector that show the custom inspector for each object in the list.

The custom editor code for the storage object looks like this:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEditor;
 
 [CustomEditor(typeof(StorageSystem))]
 public class StorageSystemPropertyDrawer : Editor
 {
     List<Editor> itemEditors = new List<Editor>();
     List<bool> foldouts = new List<bool>();
 
     private void OnEnable()
     {
         if(itemEditors.Count == 0)
         {
             foldouts.Clear();
             StorageSystem system = (StorageSystem)target;
 
             foreach (Item item in system.items)
             {
                 storageEditors.Add(Editor.CreateEditor(item));
                 foldouts.Add(false);
             }
         }
     }
 
     public override void OnInspectorGUI()
     {
         StorageSystem system = (StorageSystem)target;
 
         for (int b = 0; b < system.items.Count; b++)
         {
             foldouts[b] = EditorGUILayout.Foldout(foldouts[b], system.items[b].itemName);
 
             if(foldouts[b])
             {
                 itemEditors[b].OnInspectorGUI();
                 if (GUI.changed)
                     EditorUtility.SetDirty(target);
             }
         }
 
         if (GUILayout.Button("Add Item"))
         {
             system.items.Add(new Item());
             Debug.Log(typeof(ItemEditor));
             itemEditors.Add(Editor.CreateEditor(system.items[system.items.Count - 1]) as ItemEditor);
             foldouts.Add(false);
         }
 
         if (GUILayout.Button("Clear Items"))
         {
             system.items.Clear();
 
             itemEditors.Clear();
             foldouts.Clear();
         }
     }
 }

And the custom editor for the actual items:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEditor;
 using System;
 using System.Reflection;
 
 [CustomEditor(typeof(Item))]
 public class ItemEditor : Editor
 {
     public override void OnInspectorGUI()
     {
           //Unimportant implementation stuff
     }
 }

So the issue lies in the fact that this code causes a NullReferenceException at the following line:

 itemEditors[b].OnInspectorGUI();

Through some debugging, it appears that the actual itemEditor is null, despite the fact that a CustomEditor exists for the Item type. Any ideas as to why this might be happening?