HELP --- Object reference not set to instance of an object.

Hey guys, well it looks like i've got a problem which i don't know what it is. the console panel gives me thos error: NullReferenceException: Object reference not set to an instance of an object: on line 66 but still i can't seem to know what exactly is the issue here.

Here's the code; skip to line 66 for the error line.

 using UnityEngine;
  using System.Collections;
  using System.Collections.Generic;
  using System;
  using System.Runtime.Serialization.Formatters.Binary;
  using System.IO;
  
  
  public class SaveLoad : MonoBehaviour {
  
  
      void Start (){
  
          //Loading ();
      }
  
  
      [System.Serializable]
      public class SaveData 
      {
          
          public List <Weapon> shopList = new List<Weapon> ();
          public float money;
          public int currentWeaponID;
      }
  
          public void Saving()
      {
          SaveData data = new SaveData ();
          data.money = Manager.Currency.GetMoneyInfo ();
          data.currentWeaponID = Manager.Currency.currentWeaponId;
  
          //ADD ALL THE WEAPONS FROM THE WEAPONSHOP LIST
          for (int i = 0; i < WeaponSystem.WeaponShop.WeaponsList.Count; i++)
          {
              data.shopList.Add (WeaponSystem.WeaponShop.WeaponsList[i]);
          }
  
          BinaryFormatter bf = new BinaryFormatter ();
          FileStream stream = new FileStream (Application.persistentDataPath + "/Shop.Weapon", FileMode.Create);
  
          bf.Serialize (stream, data);
          stream.Close ();
  
          print("SAVED");
      }
  
  
      public void Loading() 
      {
          if (File.Exists (Application.persistentDataPath + "/Shop.Weapon")) 
            {
              
              BinaryFormatter bf = new BinaryFormatter ();
              FileStream stream = new FileStream (Application.persistentDataPath + "/Shop.Weapon", FileMode.Open);
  
              SaveData data = (SaveData)bf.Deserialize (stream);
              Manager.Currency.SetMoneyInfo (data.money);
              Manager.Currency.currentWeaponId = data.currentWeaponID;
  
              stream.Close ();
  
              for (int i = 0; i < data.shopList.Count; i++) 
              { 
                  //UPDATE THE SHOP
                  WeaponSystem.WeaponShop.WeaponsList [i] = data.shopList [i];   //Error is here.
  
                  //UPDATE ALL SPRITES
                  WeaponSystem.WeaponShop.UpdateSprite (WeaponSystem.WeaponShop.WeaponsList [i].WeaponID);
  
                  //UPDATE ALL BUTTONS
                  WeaponSystem.WeaponShop.UpdatBuyButtons ();
              }
          }
  
          else 
              
          {
  
              print ("No file found");
          }
      }
  
      public void Delete()
      {
          if (File.Exists (Application.persistentDataPath + "/Shop.Weapon"))
          {
              File.Exists (Application.persistentDataPath + "/Shop.Weapon");
          }
  
      }
  
  
  }

The error : ullReferenceException: Object reference not set to an instance of an object SaveLoad.Loading () (at Assets/Scripts/Shop/SaveLoad.cs:66)