C# instantiate into list

Why am I having trouble instantiating into a list? When I my script I get the following error: NullReferenceException: Object reference not set to an instance of an object. I’m using a public variable that has a game object placed in the inspector. I don’t understand why it shows as null.

public GameObject _gameObject;   
List <GameObject> _list; 
void Start(){ 
      for(int i=0; i<5; i++){
            _list.Add( (GameObject)Instantiate(_gameObject) );

You haven’t initialised your list yet…

void Start()
      _list = new List<GameObject>();
      for(int i=0; i<5; i++){
            _list.Add( (GameObject)Instantiate(_gameObject));

Have you added the this line to the top of your code?

using System.Collections.Generic;

If you have then try changing your start code to this,

void Start() {
List<GameObject> _list = new List<GameObject>();
    for(int i=0, i<5, i++) {
       GameObject thisObject = Instantiate(_gameObject) as GameObject;

I’m not entirely sure what the difference is, but that code is in the format I use and always works fine.