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

using System.Collections;
using System.Collections.Generic;
using Unity.VisualScripting;
using UnityEngine;
using UnityEngine.UI;
using UnityEngine.UIElements;
using static UnityEditor.PlayerSettings;
 
    [RequireComponent(typeof(Rigidbody))]
public class Block : MonoBehaviour
{
    
    [SerializeField]
    Item item;
    [SerializeField]
    bool usedestTool;
    playerInv pl;
    public Item destroed_tool;
    [SerializeField]
    Transform mov;
    [SerializeField]
    GameObject block;
    public string ID;
    [SerializeField]
    Texture texture;
    [SerializeField]
    int durabition;
    [SerializeField]
    GameObject mehanic;
    [SerializeField]
    GameObject Drop;
    [SerializeField]
    bool useGravity = false;
 
    void OnMouseDown()
    {
    
        durabition--;
    }
 
    void Start()
    {
        GetComponent<Renderer>().material.mainTexture = texture;
        if (useGravity)
        {
            GetComponent<Rigidbody>().useGravity = true;
        }
    }
 
    void Update()
    {
        if (durabition == 0) {
 
            Destroy(block);
 
        }
    }
    private void OnDestroy()
    {
        if (usedestTool)
        {
            if (destroed_tool.ID == pl.mainhand_tool.ID) //здесь ошибка
            {
                item.drop(Drop, mov);
 
            }
        }
        else item.drop(Drop, mov);
 
    }
}

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
[RequireComponent(typeof(BoxCollider))]
[RequireComponent(typeof(Rigidbody))]
 
public class Item : MonoBehaviour
{
 
    public Item item1;
    playerInv pl;
    public string ID;
    public GameObject item;
    public bool blockid = false;
    // Start is called before the first frame update
    void Start()
    {
        GetComponent<Rigidbody>().useGravity = true;
    }
 
    // Update is called once per frame
    void Update()
    {
        item.transform.Rotate(0, 0.1f, 0);
    }
    private void OnTriggerEnter(Collider other)
    {
        if (other.tag == "Player")
        {
            
            Destroy(item);
        }
    }
    public void OnDestroy() {
        pl.mainhand_tool = item1; //здесь ошибка
    }
    public void drop(GameObject Item,Transform pos)
    {
        Instantiate(Item, pos);
    }
}

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
 
public class playerInv : MonoBehaviour
{
    public Item mainhand_tool;
    // Start is called before the first frame update
    void Start()
    {
        
    }
 
    // Update is called once per frame
    void Update()
    {
        
    }
}