Null Reference Exception when using if(!islocalplayer) destroy

So Im a complete newbie in networking, im using a network manager. I added a destroy if not local player.

However for some reason I get a null reference exception. The network identity is set to local player authority and I added the player prefab, ticked spawn automatically in the network manager. Here's my full code:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine.Networking;
 using UnityEngine;
 
 public class player_controller : NetworkBehaviour {
     //private int DebugComment;
     private int frame;
 
     public bool onVehicle = false;
     public bool nearPlanet = false;
     public float speed;
     private Vector3 moveDirection;
     public float mouseSensitivity;
     public float clampAngle;
     //public Camera cameraOBJ;
     //public Camera minimapcameraOBJ;
     Animator droidAnim;
     Rigidbody PlayerRB;
     Transform mainCam;
     Transform miniCam;
     public Vector3 offset;
     private float rotationY = 0.0f; // rotation around the up/y axis
     private float rotationX = 0.0f; // rotation around the right/x axis
 
     void Start()
     {
         /*if (!isLocalPlayer)
         {
             destroy(this);
             return;
         }*/
         mainCam = GameObject.Find("FirstPersonCamera").GetComponent<Transform>();
         miniCam = GameObject.Find("MinimapCamera").GetComponent<Transform>();
         offset = new Vector3(0f, 1000f, 0f);
         PlayerRB = GetComponent<Rigidbody>();
         Vector3 rotation = transform.localRotation.eulerAngles;
         rotationY = rotation.y;
         rotationX = rotation.x;
         //Camera cameracopy = Instantiate<Camera>(cameraOBJ);
         //Camera minimapcameracopy = Instantiate<Camera>(minimapcameraOBJ);
     }
 
 
 
 
 
     void Update()
     {
         Debug.Log("isLocalPlayer == " + isLocalPlayer);
         //camera
         Vector3 camPos = this.transform.position;
         mainCam.transform.position = camPos;
         Vector3 miniCamPos = this.transform.position + offset;
         miniCam.transform.position = miniCamPos;
         //DebugComment++;
 
         //Outer space
         if (onVehicle == false && nearPlanet == false)
         {
 
             //rotate
                 float mouseX = Input.GetAxis("Mouse X");
                 float mouseY = -Input.GetAxis("Mouse Y");
 
                 rotationY += mouseX * mouseSensitivity * Time.deltaTime;
                 rotationX += mouseY * mouseSensitivity * Time.deltaTime;
 
                 rotationX = Mathf.Clamp(rotationX, -clampAngle, clampAngle);
 
                 if(rotationX < -30)
                 {
                     rotationX = -30;
                 }
 
                 Quaternion localRotation = Quaternion.Euler(rotationX, rotationY, 0.0f);
                 transform.rotation = localRotation;
                 //end of rotate
 
 
 
                 //move
                 moveDirection = (transform.forward * Input.GetAxis("Vertical")) + (transform.right * Input.GetAxis("Horizontal"));
                 moveDirection = moveDirection.normalized * speed;
                 if (Input.GetButton("Jump"))
                 {
                     moveDirection.y = speed;
                 }
                 if (Input.GetKey(KeyCode.LeftShift))
                 {
                     moveDirection.y = -speed;
                 }
 
                 PlayerRB.velocity = moveDirection;
 
             if(Input.GetButton("Vertical") || Input.GetButton("Horizontal") || Input.GetKey(KeyCode.LeftShift) || Input.GetButton("Jump"))
             {
                 PlayerRB.isKinematic = false;
                 if (frame > 5)
                 {
                     PlayerRB.isKinematic = true;
                     frame = 0;
                 }else
                 {
                     PlayerRB.isKinematic = false;
                     frame++;
                 }
             }else
             {
                 PlayerRB.isKinematic = true;
             }
             //end of move
         }
 
 
 
 
 
 
         //Near Planet
         if (onVehicle == false && nearPlanet == true)
         {
 
 
             //rotate
                 float mouseX = Input.GetAxis("Mouse X");
                 float mouseY = -Input.GetAxis("Mouse Y");
 
                 rotationY += mouseX * mouseSensitivity * Time.deltaTime;
                 rotationX += mouseY * mouseSensitivity * Time.deltaTime;
 
                 rotationX = Mathf.Clamp(rotationX, -clampAngle, clampAngle);
 
                 Quaternion localRotation = Quaternion.Euler(0.0f, rotationY, 0.0f);
                 transform.rotation = localRotation;
                 //end of rotate
 
 
 
         }
 
 
 
 
 
 
 
     }
 }
 

This is the error I got NullReferenceException: Object reference not set to an instance of an object player_controller.Update () (at Assets/WarpSpace/Obj/ObjFile/Droid/Scripts/player_controller.cs:52)

Thanks