NullReferenceException: Object reference Error. Please help!

I keep getting this blankety-blank error from my code:

NullReferenceException: Object reference not set to an instance of an object
Deck+<GetCards>d__2.MoveNext () (at Assets/Scripts/Deck.cs:16)
DeckView.ShowCards () (at Assets/Scripts/DeckView.cs:24)
DeckView.Start () (at Assets/Scripts/DeckView.cs:17)

Can someone look at these two classes and tell me where the exception is and how to fix it? The code works for others, but not me. I swear this is bulls&&&&t!

DECKVIEW CLASS

using System.Collections;
using System.Collections.Generic;
using UnityEditor;
using UnityEngine;
[RequireComponent(typeof(Deck))]
public class DeckView : MonoBehaviour
{
Deck deck;
public Vector3 start;
public float cardOffset;
public GameObject cardPrefab;
void Start()
{
deck = GetComponent<Deck>();
ShowCards();
}
void ShowCards()
{
int cardCount = 0;
foreach (int i in deck.GetCards())
{
float co = cardOffset * cardCount;
GameObject cardCopy = (GameObject)Instantiate(cardPrefab);
Vector3 temp = start + new Vector3(co, 0f);
cardCopy.transform.position = temp;
cardCount++;

}
}

DECK CLASS
using System.Collections.Generic;
using UnityEngine;
public class Deck : MonoBehaviour
{
List<int> cards;
void Start()
{
Shuffle();
}
public IEnumerable<int> GetCards()
{
foreach (int i in cards) <---- Problem here
{
yield return i;
}
}
public void Shuffle()
{
if (cards == null)
{
cards = new List<int>();
}
else
{
cards.Clear();
}
for (int i = 0; i < 64; i++)
{
cards.Add(i);
}
int n = cards.Count;
while (n > 1)
{
n--;
int k = Random.Range(0, n + 1);
int temp = cards[k];
cards[k] = cards[n];
cards[n] = temp;
}
}
}

 

DeckView Class:

You are missing a curly brace at the end of the script.

Deck Class:

Change the Start function to Awake.

See this link for explanation:

c # - (unity) i want to line up shuffled cards, but i get a nullreferenceexception