Double Array (Custom Editor)

Basicly, what I am trying to do, is to display a double array as one. Let me explain better.

--> First I have a list of strings

 [HideInInspector]
     public List<string> ThemesList = new List<string>();

-->Then in the custom Editor I display it as a Drop Down Menu

 GUIContent themeList = new GUIContent("Theme Mode");
     code.SelecteedThemeIndex = EditorGUILayout.Popup(themeList, code.SelecteedThemeIndex, code.ThemesList.ToArray());

(code.SelecteedThemeIndex being my choice, (everything works just fine here))

--> Now I have an array of Images

 public Image[][] ThemeArray = new Image[5][];

' 5 ' being the maximum allowed number, it may change to any other

--> to display it, In custom Editor I use

 Image[][] array = code.ThemeArray;
  
             code.showImages = EditorGUILayout.Foldout(code.showImages, "Themes List");
             if (code.showImages)
             {
                 EditorGUI.indentLevel++;
                 code.ObjectSize = Mathf.Max(0, EditorGUILayout.IntField("Size", code.ObjectSize));
  
                 for (int i = 0; i < code.ObjectSize; i++)
                 {
                     array[code.SelecteedThemeIndex][i] = (Image)EditorGUILayout.ObjectField("Theme " + i, array[code.SelecteedThemeIndex][i], typeof(Image), true);
                 }
  
                 EditorGUI.indentLevel--;
             }

I am trying to show in inspector an array of images, based on the selected Index. (ex. on Index 0, there will be 3 images (img 1, img 2, img 3) on Index 1, there will be also 3 images (img 1, img 4, img 5) and I can switch the Index through the drop down menu, and the images(aka Arrays) will be swaped) Until now, if I set the ObjectSize to anything but ' 0 ' it gives me this error

In Visual Studio (2019) there are no errors.

If you need the full code there it is:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEditor;
 using UnityEngine.UI;
  
 public class ThemesCoder : MonoBehaviour
 {
     [HideInInspector]
     public List<string> ThemesList = new List<string>();
     [HideInInspector]
     public List<Image> Theme = new List<Image>();
     [HideInInspector]
     public int SelecteedThemeIndex = 0;
     [HideInInspector]
     public bool showList = false;
     [HideInInspector]
     public bool showImages = false;
     [HideInInspector]
     public Image[][] ThemeArray = new Image[5][];
     [HideInInspector]
     public int ObjectSize = 0;
     [HideInInspector]
     public int size = 0;
  
     [CustomEditor(typeof(ThemesCoder))]
     //[CanEditMultipleObjects]
     public class ThemeCoderEditor : Editor
     {
         public override void OnInspectorGUI()
         {
             base.OnInspectorGUI();
  
             DrawInspector();
         }
  
         public void DrawInspector()
         {
             ThemesCoder code = (ThemesCoder)target;
  
             #region Themes Modes List
          
            
             code.showList = EditorGUILayout.Foldout(code.showList, "Themes List");
             if (code.showList)
             {
                 EditorGUI.indentLevel++;
                 List<string> list = code.ThemesList;
                 code.size = Mathf.Max(0, EditorGUILayout.IntField("Size", list.Count));
  
                 while (code.size > list.Count)
                 {
                     list.Add(null);
                 }
  
                 while (code.size < list.Count)
                 {
                     list.RemoveAt(list.Count - 1);
                 }
  
                 for (int i = 0; i < list.Count; i++)
                 {
                     list[i] = EditorGUILayout.TextField("Theme " + i, list[i]);
                 }
                 EditorGUI.indentLevel--;
             }
             #endregion
  
             #region Curent Mode
             GUIContent themeList = new GUIContent("Theme Mode");
             code.SelecteedThemeIndex = EditorGUILayout.Popup(themeList, code.SelecteedThemeIndex, code.ThemesList.ToArray());
             #endregion
  
             EditorGUILayout.Space();
  
             #region Theme Game Object
            
             Image[][] array = code.ThemeArray;
  
             code.showImages = EditorGUILayout.Foldout(code.showImages, "Themes List");
             if (code.showImages)
             {
                 EditorGUI.indentLevel++;
                 code.ObjectSize = Mathf.Max(0, EditorGUILayout.IntField("Size", code.ObjectSize));
  
                 for (int i = 0; i < code.ObjectSize; i++)
                 {
                     array[code.SelecteedThemeIndex][i] = (Image)EditorGUILayout.ObjectField("Theme " + i, array[code.SelecteedThemeIndex][i], typeof(Image), true);
                 }
  
                 EditorGUI.indentLevel--;
             }
             #endregion
         }
     }
 }

Edit: I will use sprites, not Images as arrays, shall be no difference in the code.

I tried aproaching this problem with a struct:

 [System.Serializable]
 public struct SpriteArray
 {
     public Sprite[] Sprites;
 }

Then declaring it like this

 [HideInInspector]
     public SpriteArray[] ThemeArray;

Using the next loop to show it

 for (int i = 0; i < code.ObjectSize; i++)
                 {
                     array[code.SelecteedThemeIndex].Sprites[i] = (Sprite)EditorGUILayout.ObjectField("Theme " + i, array[code.SelecteedThemeIndex].Sprites[i], typeof(Sprite), true);
                 }

Still I get no errors in VS, only when I change the ObjectSize to anything but 0 I get the same error as above.