菜鸟求助！关于第三人称摄像机控制的问题

代码如下：
using UnityEngine;
using System.Collections;
//添加脚本到component菜单
[AddComponentMenu("CameraControl/Follow")]
public class cameraFollower : MonoBehaviour
{
//摄像机固定在猪脚上方10米高度
public float camera_height = 10.0f;
//摄像机离猪脚大概10米的水平距离
public float camera_distance = 10.0f;
//摄像机和猪脚的transform属性
private Transform player;
private Transform camera;
// Use this for initialization
void Start()
{
//初始化
player = GameObject.FindGameObjectWithTag("Player").transform;
camera = Camera.main.transform;
}
// Update is called once per frame
void Update()
{
//看向猪脚
//camera.LookAt (player);
//与猪脚的正前方为正前方(只取Y轴的旋转度)
camera.eulerAngles = new Vector3(camera.eulerAngles.x,player.eulerAngles.y,camera.eulerAngles.z);
//获取当前的镜头的Y轴旋转度
float angle = camera.eulerAngles.y;
//计算x轴的距离差:
float deltaX = camera_distance * Mathf.Sin(angle * Mathf.PI / 180);
float deltaZ = camera_distance * Mathf.Cos(angle * Mathf.PI / 180);
//每一帧都改变摄像机的高度
camera.position = new Vector3(player.position.x - deltaX,
player.position.y + camera_height,
player.position.z - deltaZ);
Debug.Log("angle:" + angle + ",deltax:" + deltaX + ",deltaZ:" + deltaZ);
}
}
在
camera.eulerAngles = new Vector3(camera.eulerAngles.x,player.eulerAngles.y,camera.eulerAngles.z); 这一行会报错，Object reference not set to an instance of an object，我知道这是说没有实例化，可是我不知道到底是哪里的问题啊？