how to fix object reference not set to an instance of an object in unity

Question

This is my code:

public class CameraRotation : MonoBehaviour
{
PlayerMovement moveScript;

void Update()
{
 if(moveScript.canMove == true){
 console.Log("I Can Move");
 }
 }
}

If I run it, I'm getting this error

object reference not set to an instance of an object