Object reference not set to an instance of an object

using UnityEngine;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Runtime.Serialization.Formatters.Binary;

public class SaveManager : MonoBehaviour {
    public List<object> SaveObjs = new List<object>();

    public Item P1_Hand;
    public Item P2_Hand;
    public Item P3_Hand;

    public List<Item> P1_Inventory = new List<Item>();
    public List<Item> P2_Inventory = new List<Item>();
    public List<Item> P3_Inventory = new List<Item>();

    public List<SerializableChest> chests = new List<SerializableChest>();

    string path = @"\Save.tgtayt";

    public static SaveManager Instance;

    void Awake()
    {
        Instance = this;
        Load();
    }

    public void Save()
    {
        SaveObjs.Add(P1_Hand.Name);
        SaveObjs.Add(P2_Hand.Name);
        SaveObjs.Add(P3_Hand.Name);

        List<string> P1_String = new List<string>();
        foreach (Item i in P1_Inventory)
        {
            P1_String.Add(i.Name);
        }
        List<string> P2_String = new List<string>();
        foreach (Item i in P2_Inventory)
        {
            P2_String.Add(i.Name);
        }
        List<string> P3_String = new List<string>();
        foreach (Item i in P3_Inventory)
        {
            P3_String.Add(i.Name);
        }

        SaveObjs.Add(P1_String);
        SaveObjs.Add(P2_String);
        SaveObjs.Add(P3_String);
        SaveObjs.Add(chests);
        byte[] b = Serialize();
        File.WriteAllBytes(Application.persistentDataPath + path, b);
        Debug.Log(Application.persistentDataPath + path);
    }

    public void Load()
    {
        byte[] b = File.ReadAllBytes(Application.persistentDataPath + path);
        List<object> o = DeSerialize(b);
        P1_Hand = o[0] as Item;
        P2_Hand = o[1] as Item;
        P3_Hand = o[2] as Item;

        List<string> P1_String = new List<string>();
        P1_String = (List<string>)o[3];

        List<Item> P1_i = new List<Item>();

        foreach (string str in P1_String)
        {
            P1_i.Add(GameManager.Instance.FindItem(str));
        }

        P1_Inventory = P1_i;

        List<string> P2_String = new List<string>();
        P2_String = (List<string>)o[4];

        List<Item> P2_i = new List<Item>();

        foreach (string str in P2_String)
        {
            P2_i.Add(GameManager.Instance.FindItem(str));
        }

        P2_Inventory = P2_i;

        List<string> P3_String = new List<string>();
        P3_String = (List<string>)o[5];

        List<Item> P3_i = new List<Item>();

        foreach (string str in P3_String)
        {
            P3_i.Add(GameManager.Instance.FindItem(str));
        }

        P3_Inventory = P3_i;

        chests = (List<SerializableChest>)o[6];

        GameManager.Instance.Characters[0].Instance.Inventory = P1_Inventory;
        GameManager.Instance.Characters[0].Instance.InHand = P1_Hand;

        GameManager.Instance.Characters[1].Instance.Inventory = P2_Inventory;
        GameManager.Instance.Characters[1].Instance.InHand = P2_Hand;

        GameManager.Instance.Characters[2].Instance.Inventory = P3_Inventory;
        GameManager.Instance.Characters[3].Instance.InHand = P3_Hand;

    }

    byte[] Serialize()
    {
        BinaryFormatter bf = new BinaryFormatter();
        MemoryStream ms = new MemoryStream();
        bf.Serialize(ms, SaveObjs);
        return ms.ToArray();
    }

    List<object> DeSerialize(byte[] b)
    {
        MemoryStream ms = new MemoryStream();
        BinaryFormatter bf = new BinaryFormatter();
        ms.Write(b, 0, b.Length);
        ms.Seek(0, SeekOrigin.Begin);
        List<object> obj = (List<object>)bf.Deserialize(ms);
        return obj;
    }
}