GUILayout.Button problems

Hey guys. I wanted to make a system that added a new gameobject to a list. The specific gameobject is assigned to a gui button in the editor. But every time a press the button in the editor I get an error.


Send help pls

Code (CSharp):

1. public class DialogNPC : MonoBehaviour
2. {
3.     public GameObject[] speaker;
4.  
5.     public List<Converation> conv;
6.     public Choises[] choises;
7.  
8.    
9.  
10.     int nrOfConv;
11.     bool backAndForth = true;
12.  
13.     //private AudioSource[] speakersAudio;
14.  
15.     Converation con;
16.     public void makeConvForSpeaker(GameObject speaker)
17.     {
18.         con.who = speaker;
19.         conv.Add(con);
20.     }
21. }

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. using UnityEditor;
5.  
6. [CustomEditor(typeof(DialogNPC))]
7. public class DialogSystemEditor : Editor
8. {
9.     public override void OnInspectorGUI()
10.     {
11.         base.OnInspectorGUI();
12.  
13.         DialogNPC npc = (DialogNPC)target;
14.  
15.         for (int i = 0; i < npc.speaker.Length; i++)
16.             if (GUILayout.Button(npc.speaker[i].name))
17.                 npc.makeConvForSpeaker(npc.speaker[i]);
18.  
19.  
20.     }
21. }
22.  

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class Converation : MonoBehaviour
6. {
7.     public string theLine;
8.     public GameObject who;
9.     public AudioClip audio;
10. }
11.  

 

This is the error btw

Thanks