Unity NullReferenceException - ＆gt;不明白为什么

Question

几个小时我现在遇到这些问题：

  

NullReferenceException：未将对象引用设置为对象的实例   EnemyScreenSpaceUIScript.Start（）（在Assets / Scripts / EnemyScreenSpaceUIScript.cs：34）

     

NullReferenceException：未将对象引用设置为对象的实例   EnemyScreenSpaceUIScript.Update（）（在Assets / Scripts / EnemyScreenSpaceUIScript.cs：47）

第34行在Start（） - Method（我添加了注释）

第47行是Update（） - Method

中的第一行

这是我的EnemyScreenSpaceUIScript：

public EnemyScript enemyScript;

public Canvas canvas;
public GameObject healthPrefab;

public float healthPanelOffset = 0.35f;
public GameObject healthPanel;
public Text enemyName;
private Slider healthSlider;

private DepthUIScript depthUIScript;

private Renderer selfRenderer;


// Use this for initialization
void Start () 
{
    GameObject CanvasObj = GameObject.Find("HealthPrefab");
    canvas = CanvasObj.GetComponent<Canvas>();

    enemyScript = GetComponent<EnemyScript>();
    healthPanel = Instantiate(healthPrefab) as GameObject;
    healthPanel.transform.SetParent(canvas.transform, false);

    enemyName = healthPanel.GetComponentInChildren<Text>();
    enemyName.text = enemyScript.monsterName; // <- this is line 34

    healthSlider = healthPanel.GetComponentInChildren<Slider>();

    depthUIScript = healthPanel.GetComponent<DepthUIScript>();
    canvas.GetComponent<ScreenSpaceCanvasScript>().AddToCanvas(healthPanel);

    selfRenderer = GetComponentInChildren<Renderer>();
}

// Update is called once per frame
void Update () 
{
    healthSlider.value = enemyScript.HP / (float)enemyScript.maxHP; //<- this is line 47

    Vector3 worldPos = new Vector3(transform.position.x, transform.position.y + healthPanelOffset, transform.position.z);
    Vector3 screenPos = Camera.main.WorldToScreenPoint(worldPos);
    healthPanel.transform.position = new Vector3(screenPos.x, screenPos.y, screenPos.z);

    float distance = (worldPos - Camera.main.transform.position).magnitude;
    depthUIScript.depth = -distance;

    float alpha = 3 - distance / 4.0f;
    depthUIScript.SetAlpha(alpha);

    if (selfRenderer.isVisible && alpha > 0)
    {
        healthPanel.SetActive(true);
    }
    else
    {
        healthPanel.SetActive(false);            
    } 

    if (gameObject.GetComponent<Mob>().health <= 0)
    {
        healthPanel.SetActive(false);
    }
    else
    {

    }
}

我无法弄清楚出了什么问题？