NullReferenceException Help please :>

Well, yeah. im following Gamer To Game Developers tutorial on making a game and im in chapter 2

Im getting this error: NullReferenceException: Object reference not set to an instance of an object Solution 'FPSSingleplayer' ‎(2 projects) Assets/GAMES/Scripts/Masters/GameManager_TogglePauseMenu.cs 39

Heres my code, line, it points at the if() statement even though GTGD did the same thing as me, maybe its outdated or maybe i made a typo, it also gives me the same error for line 50, and 13.

 using UnityEngine;
 using System.Collections;
 
 namespace Chapter2
 {
 public class GameManager_TogglePauseMenu : MonoBehaviour
 {
 private GameManagerMaster gameManagerMaster;
 public GameObject menu;
 
 void Start()
 {
 ToggleMenu();
 }
 
 void Update()
 {
 CheckForMenuToggleRequest();
 }
 
 void onEnable()
 {
 SetInitialReferences();
 gameManagerMaster.GameOverEvent += ToggleMenu;
 }
 
 void onDisable()
 {
 gameManagerMaster.GameOverEvent -= ToggleMenu;
 }
 
 void SetInitialReferences()
 {
 gameManagerMaster = GetComponent();
 }
 
 void CheckForMenuToggleRequest()
 {
 if (Input.GetKeyUp(KeyCode.Escape)&& !gameManagerMaster.isGameOver && !gameManagerMaster.isInventoryUIOn)
 {
 ToggleMenu();
 }
 }
 
 void ToggleMenu()
 {
 if (menu != null)
 {
 menu.SetActive(!menu.activeSelf);
 gameManagerMaster.isMenuOn = !gameManagerMaster.isMenuOn;
 gameManagerMaster.CallEventMenuToggle();
 Debug.LogWarning("Wierd");
 }
 else
 {
 Debug.LogWarning("You didn't define the menu! Silly!");
 }
 }
 }
 }