Can't add GameObjects to a List

Questions & Answers
1

I am writing a dungeon generator. Its in very early stages. I got it to detect 1 exit node and spawn a hall tile and a room tile beyond that. An exit node is an empty GameObject. Now I want to make a list to store more then one exit node. I can then later iterate through all the nodes and spawn halls and rooms. I am stuck at this error:

NullReferenceException: Object reference not set to an instance of an object
Dungeon.AddNodes (UnityEngine.Transform nodes) (at Assets/Dungeon.cs:47)
Dungeon.FindNodes () (at Assets/Dungeon.cs:41)
Dungeon.Start () (at Assets/Dungeon.cs:19)

Here is the code:

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

public class Dungeon : MonoBehaviour {
	
	public GameObject start;  //holds the start tile
	public GameObject player; //holds the player pawn
	public GameObject halls;  //holds the hall tiles, will be changed to an array later.
	public GameObject rooms;  //holds the room tiles, will be changed to an array later.
	
	
	private List<Transform> exitNodes; //holds the current nodes, will be updated after each iteration of room generation.
	
	
	
	// Use this for initialization
	void Start () {
		CreateStart();
		FindNodes();		
		SpawnDungeon();
	}
	
	// Update is called once per frame
	void Update () {
	
	}
	
	private void CreateStart()
	{
		//creates the starting tile and player pawn.
		GameObject go = Instantiate(start, Vector3.zero, Quaternion.identity) as GameObject; 
		GameObject pc = Instantiate(player, Vector3.up, Quaternion.identity) as GameObject;
	}
	

	
	private void FindNodes()
	{
		//Finds all nodes tagged for the north side of the tile, indicating a positive x translation.
		GameObject[] node = GameObject.FindGameObjectsWithTag("N_exit");
		foreach(GameObject temp in node)
		{
			// adds the nodes to exitNode list, not working...
			exitNodes.Add(temp.transform);
		}
	}
	
	
	
	private void SpawnDungeon()
	{
		// Vector3.zero will become the location of the current node.
		GameObject spawn = Instantiate(halls, Vector3.zero, Quaternion.identity) as GameObject;
		//translate to the proper offset.
		spawn.transform.Translate(2.5f,0,0);
		//Vector3.zero will become the location of the current node.
		spawn = Instantiate(rooms, Vector3.zero, Quaternion.identity) as GameObject;
		//translate to the proper offset.
		spawn.transform.Translate(10,0,0);
	}
}
2

You have only declared the list but not instantiated it.

You can instantiate the List in Start () method:

 void Start () {
    exitNodes = new List<Transform> ();
    CreateStart();
    FindNodes();
    SpawnDungeon();
}
3

Doh! I knew it was going to be a n00b mistake! Thanks a bunch.