Null Reference Exception error on GameObject.SendMessage

Hey guys, i have this script to pickup items, and works perfectly, but this Null Reference Exception error comes from line 60 and i don't know the reason. Any help please ?

 using UnityEngine;
 using System;
 using System.Collections;
 using System.Collections.Generic;
 
     [System.Serializable]
     public class TagsClass{
         public string m_InteractTag = "Interact";
         public string m_InteractItemsTag = "InteractItem"; 
         public string m_DoorsTag = "Door"; 
     }
 
 public class DragRigidbodyUse : MonoBehaviour {
     
     public GameObject playerCam;
     
     public string UseButton = "Use";
     public TagsClass Tags = new TagsClass();
     
     private float PickupRange = 2f;
     
     private Ray playerAim;
     private GameObject objectHeld;
     private bool tryPickupObject;
     
     void Start () {
         tryPickupObject = false;
         objectHeld = null;
     }
     
     void FixedUpdate () {
         if(Input.GetButton(UseButton)){
             tryPickObject();
             tryPickupObject = false;
             Use();
         }
     }
     
     private void tryPickObject(){
         Ray playerAim = playerCam.GetComponent<Camera>().ViewportPointToRay(new Vector3(0.5f, 0.5f, 0));
         RaycastHit hit;
         
         if (Physics.Raycast (playerAim, out hit, PickupRange)){
             objectHeld = hit.collider.gameObject;
             if(hit.collider.tag == Tags.m_InteractTag && tryPickupObject){
                 objectHeld.GetComponent<Rigidbody>().useGravity = false;
                 /**/
             }
             if(hit.collider.tag == Tags.m_InteractItemsTag && tryPickupObject){
                 objectHeld.GetComponent<Rigidbody>().useGravity = true;
             }
             if(hit.collider.tag == Tags.m_DoorsTag && tryPickupObject){
                 objectHeld.GetComponent<Rigidbody>().useGravity = true;
                 objectHeld.GetComponent<Rigidbody>().freezeRotation = false;
             }
         }
     }
     
     private void Use() {
         objectHeld.SendMessage ("UseObject",SendMessageOptions.DontRequireReceiver); //Every script attached to the PickupObject that has a UseObject function will be called.
         objectHeld = null;    
     }
 }