＆＃34; C＃NullReferenceException：对象引用未设置为对象的实例＆＃34;访问父标签时

Question

我正在尝试获取对手父母的标签：

  _____Hierarchy_____
 | EmptyGameObject   | <-- Has the tag "Generator"
 |   ColliderObject  | <-- Gets hit by Raycast (Has the collider)
 |___________________|

但是我收到了错误。我不知道如何解决它。

错误在第1行

else if (hit.collider.transform.parent.gameObject.tag == "Generator" && Input.GetKeyDown ("e"))

脚本：

else if (hit.collider.transform.parent.gameObject.tag == "Generator" && Input.GetKeyDown ("e"))
{
    if (Fuel >= 100)
    {
        Fuel -= 100;
        Generator.Machine_Fuel += 100;
        ES2.Save(Fuel,  "Data/Player/Inventory/Fuel.txt");
        Debug.Log ("100ml Fuel added to machine");
        // txtRef.text = "Apples: " + apples;
    }
    else
    {
        Generator.Machine_Fuel += Fuel;
        Fuel -= Fuel;
    }
}

谢谢！

-shinevision