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

Unity Engine
,
1

Hey im trying to make the player moves to where i click in the map and its showing me this error at line 20

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.AI;

public class PlayerMovement : MonoBehaviour {
    NavMeshAgent agent;

    void Start()
    {
        agent = GetComponent<NavMeshAgent>();
    }

    void Update()
    {
        if (Input.GetMouseButtonDown(0))
        {
            RaycastHit hit;

            if (Physics.Raycast(Camera.main.ScreenPointToRay(Input.mousePosition), out hit, 100))
            {
                agent.destination = hit.point;
            }
        }

    }
}
2

Make dure you have a camera in your scene that has a MainCamera tag on it, else Camera.main won’t find anything.