I need help I can't find the error in my code!

So I am coding a dialogue system and everything is going perfectly fine until Unity said error void doesn't work. So I tried all of this other stuff and I can't seem to fix it. Can someone please help!

using System.Collections; using System.Collections.Generic; using UnityEngine;

public class DialogueSystem : MonoBehaviour {

 public static DialogueSystem Instance { get; set; }

 public List<string> dialogueLines = new List<string>();

 void Awake () {
     if (Instance != null && Instance != this)
     {
         Destroy(gameObject);
     }
     else
     {
         Instance = this;
     }
     
 }    

}

 public void AddNewDialogue(string[] lines)
 {
     dialogueLines = new List<string>();
     foreach(string line in lines)
     {
         dialogueLines.Add(line);
     }
     Debug.Log(dialogueLines.Count);
 }

}