Reference to Null object Help beginner question

NullReferenceException: Object reference not set to an instance of an object PlayerController.Update () (at Assets/Scripts/PlayerController.cs:23) I got stuck while trying to follow this tutorial https://www.youtube.com/watch?v=poeXGuQ7eUo here is code: using UnityEngine; using System.Collections;

 public enum SwipeDirection
 {
     None = 0,
     Left = 1,
     Right = 2,
     Up = 4,
     Down = 8,
 
 }
 public class SwipeManager : MonoBehaviour {
     private static SwipeManager instance;
     public static SwipeManager Instance{get {return instance;}}
     public SwipeDirection Direction{set; get;}
 
     private Vector3 touchPosition;
     private float swipeResistanceX = 50.0f;
     private float swipeResistanceY = 100.0f;
     private void start(){
         instance = this;
     }
     private void Update()
     {
         Direction = SwipeDirection.None;
         if (Input.GetMouseButtonDown (0)) {
             touchPosition = Input.mousePosition;
         }
         if (Input.GetMouseButtonUp (0)) {
             Vector2 deltaSwipe = touchPosition - Input.mousePosition;
             if (Mathf.Abs (deltaSwipe.x) > swipeResistanceX) {
                 Direction |= (deltaSwipe.x < 0) ? SwipeDirection.Right : SwipeDirection.Left;
             }
             if (Mathf.Abs (deltaSwipe.y) > swipeResistanceY) {
                 Direction |= (deltaSwipe.y < 0) ? SwipeDirection.Up : SwipeDirection.Down;
             }
         }
 
 
     }
     public bool IsSwiping(SwipeDirection dir)
     {
         return (Direction & dir) == dir;
 }
 }

 using UnityEngine;
 using System.Collections;
 
 public class PlayerController : MonoBehaviour {
 
     public float minSwipeDistY;
 
     public float minSwipeDistX;
 
     private Vector2 startPos;
     Animator animator;
     // Use this for initialization
     void Start () {
         animator = GetComponent<Animator> ();
 
     }
     
     // Update is called once per frame
     void Update () {
         if (animator.GetInteger ("Action") != 0){
             animator.SetInteger ("Action", 0);
         }
         if (SwipeManager.Instance.IsSwiping(SwipeDirection.Down)){
             animator.SetInteger ("Action", -1);
             }    
 
 
     }
 
 }
 

Both scripts are applied to my player object if that helps