MessagingSystem causes a NullReferenceException

我决定在我的项目中实现一个简单的消息传递系统。我正在使用这个:CSharpMessenger Extended(它是用静态方法实现的)。

很奇怪，当我直接调用一个方法时，一切都正常工作。但是当我用消息传递系统广播消息时，我在一些游戏对象上得到了NullReferenceException。令我惊讶的是，添加if (_gameObject == null) return;行解决了这个问题。然而，它不是一个选项，以增加一个检查，如果对象是空的每一个地方，我得到这个异常。

可能是什么问题?

下面是我广播消息的代码:

public class Head : MonoBehaviour {
    public Snake snake;
    void OnControllerColliderHit (ControllerColliderHit hit)
    {
        if ( hit.gameObject.GetComponent<Terrain>() )
            return;
            //This way everything was working without any surprises.
            //snake.PropCollected( hit.gameObject.GetComponent<Prop>() );
            //Using messaging system instead
        if ( hit.gameObject.GetComponent<Prop>() )
            Messenger<Prop>.Broadcast( "prop collected", hit.gameObject.GetComponent<Prop>() );
            Destroy(hit.gameObject);
        }
    }

订阅事件和响应事件的方法如下:

public class Snake : MonoBehaviour {
    public GameObject headBlock;
    public GameObject snakeBlocks;
    int lastSnakeBlockId;
    private GameObject FindBlockWithId( int _id )
    {
            if (!snakeBlocks) return null;    //This line somehow solves the problem; However the object is 100% assigned in the editor.
            foreach (Transform child in snakeBlocks.transform) {
                if (child.gameObject.GetComponent<SnakeBlockScript>().blockId == _id)
                {
                    return child.gameObject;
                }
            }
        return headBlock;
    }
    void Awake()
    {
        //Set up message listeners
        Messenger<Prop>.AddListener("prop collected", AddBlock);    
    }
    public void AddBlock(Prop _prop)
    {
        GameObject lastBlock = FindBlockWithId(lastSnakeBlockId - 1);
        if (!lastBlock) return;
        //Some more code
        //...
    }
}

谢谢!

snakeBlocks = null;
//Do some stuff.
snakeBlocks = someNewInstanceOfGameObject;