isLocalPlayer giving error in mirror

So i have this code for my spaceship and its giving me error on line 31 wheres there an is local player if statement,Here’s the code

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using Mirror;

public class CameraLook : NetworkBehaviour
{
    private Vector3 rotation;
    public float lookSpeed;
    public GameObject GameObjectTransform;
    public GameObject Camera;

    public float lookXLimit = 60.0f;
    public float ZoomAmount = 0;
    public float MaxToClamp = 100;
    public float ROTSpeed = 10;
    public Transform camTransform;
    public float shakeAmount;
    public ParticleSystem particle;
    private ParticleSystem pscom;
    public GameObject spaceship;
    private FOUDemo fou;
    void Start()
    {
        fou = spaceship.GetComponent<FOUDemo>();
        pscom = particle.GetComponent<ParticleSystem>();
  
    }
    void Update()
    {
        if (isLocalPlayer) //error here
        {
            if (Input.GetMouseButton(1))
            {
                rotation.y += Input.GetAxis("Mouse X") * lookSpeed;
                rotation.x += -Input.GetAxis("Mouse Y") * lookSpeed;
                rotation.x = Mathf.Clamp(rotation.x, -lookXLimit, lookXLimit);
                GameObjectTransform.transform.localRotation = Quaternion.Euler(rotation.x, rotation.y, 0);
            }
            ZoomAmount += Input.GetAxis("Mouse ScrollWheel");
            ZoomAmount = Mathf.Clamp(ZoomAmount, -MaxToClamp, MaxToClamp);
            var translate = Mathf.Min(Mathf.Abs(Input.GetAxis("Mouse ScrollWheel")), MaxToClamp - Mathf.Abs(ZoomAmount));
            Camera.transform.Translate(0, 0, translate * ROTSpeed * Mathf.Sign(Input.GetAxis("Mouse ScrollWheel")));
            if (Input.GetKey("space"))
            {

                var emission = pscom.emission;
                emission.enabled = true;
                fou.velocity = 5000;
            }
            if (Input.GetKeyUp("space"))
            {
                var emission = pscom.emission;
                emission.enabled = false;
                fou.velocity = 500;

            }
            if (Input.GetKey("w"))
            {

                fou.thrust = fou.thrust + 1;

            }
            if (Input.GetKey("s"))
            {

                fou.thrust = fou.thrust - 1;

            }
        }
    }
}

The error is in mirror islocal player checker and it was called by this
The error is NullReferenceException: Object reference not set to an instance of an object
when i already put a network identity and a network transform on it

Solved,It turn out any script that’s use local player must be inthe same game object that has Network identity