NullReferenceException: Object reference not set to an instance of an object

Hello. I'm new to Unity and C#. I get this error when I want my chest to open.
Here is the code:

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

public class Chest : MonoBehaviour {

public bool playerInRange;
public GameObject item;
private Animator animator;

public void AcilSusamAcil()
{
if (playerInRange)
{
item.SetActive(true);
animator.SetBool("isOpen", true);

}
}

private void OnTriggerEnter2D(Collider2D other)
{
if (other.gameObject.tag == ("Player"))
{
playerInRange = true;
}

}

private void OnTriggerExit2D(Collider2D other)
{
if (other.gameObject.tag == ("Player"))
{
playerInRange = false;
}
}
}


This is the error message:
NullReferenceException: Object reference not set to an instance of an object
Chest.AcilSusamAcil () (at Assets/Scripts/Chest.cs:16)
UnityEngine.Events.InvokableCall.Invoke () (at C:/buildslave/unity/build/Runtime/Export/UnityEvent.cs:166)
UnityEngine.Events.UnityEvent.Invoke () (at C:/buildslave/unity/build/Runtime/Export/UnityEvent_0.cs:58)
UnityEngine.UI.Button.Press () (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/UI/Core/Button.cs:36)
UnityEngine.UI.Button.OnPointerClick (UnityEngine.EventSystems.PointerEventData eventData) (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/UI/Core/Button.cs:45)
UnityEngine.EventSystems.ExecuteEvents.Execute (IPointerClickHandler handler, UnityEngine.EventSystems.BaseEventData eventData) (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/EventSystem/ExecuteEvents.cs:50)
UnityEngine.EventSystems.ExecuteEvents.Execute[IPointerClickHandler] (UnityEngine.GameObject target, UnityEngine.EventSystems.BaseEventData eventData, UnityEngine.EventSystems.EventFunction`1 functor) (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/EventSystem/ExecuteEvents.cs:261)
UnityEngine.EventSystems.EventSystem:Update()

 

WOW! Thank you, that helped me a lot!

 

help me pls, same error...
public static IEnumerable<Level> GetLevels(GameMode mode)
{

return Instance._modeAndLevels[mode];


}
on this line....


and all script

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

public partial class ResourceManager : Singleton<ResourceManager>
{

public static event Action<int> CoinsChanged;
#if IN_APP
public static event Action<string> ProductPurchased;
public static event Action<bool> ProductRestored;
#endif



public static bool EnableAds
{
get => PrefManager.GetBool(nameof(EnableAds), true);
set => PrefManager.SetBool(nameof(EnableAds), value);
}

public static string NoAdsProductId => GameSettings.Default.InAppSetting.removeAdsId;

public static int Coins
{
get => PrefManager.GetInt(nameof(Coins));
set
{
PrefManager.SetInt(nameof(Coins),value);
CoinsChanged?.Invoke(value);
}
}

protected override void OnInit()
{
base.OnInit();
InitLevels();
#if IN_APP
Purchaser = new Purchaser(new List<string>(), new[] { NoAdsProductId });
Purchaser.RestorePurchased += PurchaserOnRestorePurchased;
#endif
}

#if IN_APP




public static bool AbleToRestore => EnableAds;

public Purchaser Purchaser { get; private set; }


private void PurchaserOnRestorePurchased(bool success)
{
if (EnableAds && Purchaser.ItemAlreadyPurchased(NoAdsProductId))
{
EnableAds = false;
ProductPurchased?.Invoke(NoAdsProductId);
}
ProductRestored?.Invoke(success);
}


public static void RestorePurchase()
{
Instance.Purchaser.Restore();
}

public static void PurchaseNoAds(Action<bool> completed = null)
{
if (!EnableAds)
{
return;
}

Instance.Purchaser.BuyProduct(NoAdsProductId, success =>
{
if (success)
{
EnableAds = false;
}
completed?.Invoke(success);
if (success)
ProductPurchased?.Invoke(NoAdsProductId);
});
}
#endif
}


public partial class ResourceManager
{
[SerializeField]private List<TextAsset> _modeLvlAssets = new List<TextAsset>();

private readonly Dictionary<GameMode,List<Level>> _modeAndLevels = new Dictionary<GameMode, List<Level>>();

private void InitLevels()
{
for (var i = 0; i < _modeLvlAssets.Count; i++)
{
_modeAndLevels.Add((GameMode)i, JsonUtility.FromJson<LevelGroup>(_modeLvlAssets.text).ToList());
}
}

public static IEnumerable<Level> GetLevels(GameMode mode)
{

return Instance._modeAndLevels[mode];


}

public static Level GetLevel(GameMode mode,int no)
{
if(no>=Instance._modeAndLevels[mode].Count)
return new Level();
return Instance._modeAndLevels[mode][no-1];
}

public static bool IsLevelLocked(GameMode mode, int no)
{
var completedLevel = GetCompletedLevel(mode);

return no > completedLevel + 1;
}

public static int GetCompletedLevel(GameMode mode)
{
return PrefManager.GetInt($"{mode}_Level_Complete");
}

public static void CompleteLevel(GameMode mode, int lvl)
{
if (GetLevel(mode).no>lvl)
{
return;
}

PrefManager.SetInt($"{mode}_Level_Complete",lvl);
}

public static bool HasLevel(GameMode mode, int lvl) => GetLevels(mode).Count() >= lvl;

public static Level GetLevel(GameMode mode)
{
return GetLevel(mode,PrefManager.GetInt($"{mode}_Level_Complete")+1);
}
}

public enum GameMode
{
Easy,Normal,Hard
}