EntityArchetype and ScriptableObject

Hello,

I try to make an UnityEditor for a scriptable object that will be use to create an EntityArchetype. The goal is to define a list of ComponentType directly in the inspector.

I managed to get array to all ComponentType that use the interface IComponentData. With that I create a list of buttons to add the selected ComponentType to the list that will be use to create the EntityArchetype.

But I have a problem, when a try to add the selected type to a list I got the famous NullReferenceException here: componentTypes.Add(type);

Do you guys have any tips to solve this?

 using Unity.Entities;
 using UnityEngine;
 
 [CreateAssetMenu(fileName = "New Entity Setting", menuName = "EntitySetting", order = 1)]
 public class EntitySetting : ScriptableObject
 {
     public ComponentType[] types ;
 }

 using System;
 using System.Collections.Generic;
 using Unity.Entities;
 using UnityEngine;
 using UnityEditor;
 
 [CustomEditor(typeof(EntitySetting))]
 public class EntitySettingEditor : Editor
 {
     public Type[] typesAvailable;
     EntitySetting entitySetting;
 
     public void OnEnable()
     {
         entitySetting = (EntitySetting) target;
     }
 
     public override void OnInspectorGUI()
     {
         base.OnInspectorGUI();
 
         if (entitySetting.types != null)
         {
             for (int i = 0; i < entitySetting.types.Length; i++)
             {
                 GUILayout.TextArea(entitySetting.types[i].ToString());
             }
         }
 
         typesAvailable = AppDomain.CurrentDomain.GetAllInterfaceOfType(typeof(IComponentData));
 
         foreach (var type in typesAvailable)
         {
             if (GUILayout.Button(type.ToString()))
             {
                 AddThisType(type);
             }
         }
     }
 
     public void AddThisType(Type type)
     {
 
         if (entitySetting.types == null)
         {
             entitySetting.types = new ComponentType[0];
         }
 
         List<ComponentType> componentTypes = new List<ComponentType>();
 
         for (int i = 0; i < entitySetting.types.Length; i++)
         {
             componentTypes.Add(entitySetting.types[i]);
         }
 
         componentTypes.Add(type);
 
         entitySetting.types = componentTypes.ToArray();
     }
 }