how to work with custom classes that have arrays of custom classes within

I made a script that generates items from a file, then these items are stored in different books but I get errors when creating a new book and try to store an item in.

what am I doing wrong??

Code (CSharp):

1. using UnityEngine;
2. using System.Collections;
3. using System.Collections.Generic;
4.  
5.  
6. //=================================//
7. public class BooksGenerator3: MonoBehaviour {
8.    
9.     public TextAsset TextData = null;
10.     private string[] strData; // = "item1+102+M7,M8,M9,I15,I16,I17,I18,J8,J9,J10/item2+103+I14,I15,I16,I17,V14,V15,V16,V17,V18/";
11.    
12.     [System.Serializable]
13.     public class ITEM {      
14.         public string[] itemData = new string[2];
15.         public string[] words;
16.     }
17.     [System.Serializable]
18.     public class BOOK {      
19.         public ITEM[] items;
20.     }
21.    
22.     public BOOK[] inventory;
23.     public ITEM[] items;
24.    
25.     //=================================//
26.     void Start () {
27.        
28.         strData = TextData.text.Split(new char[] {'/'});
29.         items = processItems(strData);
30.         inventory = generateBooks(items);
31.        
32.         for(int x=0; x<inventory.Length; x++) {
33.            
34.             print("curBook: " + inventory[x].ITEM.itemData);
35.         }
36.        
37.     }
38.     //=================================//
39.     public ITEM[] processItems(string[] strData)  {
40.        
41.         ITEM[] tempItems = new ITEM[strData.Length];      
42.        
43.         for(int s=0; s<strData.Length; s++) {
44.             string[] curData = strData[s].Split(new char[] {'+'});
45.        
46.             ITEM newItem = new ITEM();
47.             newItem.itemData[0] = curData[0];
48.             newItem.itemData[1] = curData[1];
49.             newItem.words = curData[2].Split(new char[] {','});
50.             tempItems[s] = newItem;
51.            
52.         }
53.         return tempItems;
54.     }
55.     //=================================//
56.     public BOOK[] generateBooks(ITEM[] Items) {
57.  
58.         ArrayList firstBooks = new ArrayList();
59.  
60.         for(int i=0; i<Items.Length; i++) {          
61.             BOOK tempBook = new BOOK();
62.             tempBook.items[i] = Items[i];
63.             firstBooks.Add(tempBook);
64.         }
65.         return firstBooks.ToArray(typeof(BOOK)) as BOOK[];  
66.     }
67.  
68. }
69.  

and the file contains this

with this file two items are created with your data