c# -对象变量赋值失败

我很难理解为什么我的变量有一个空值。

这是我的类构造函数:

private GraphNode current;
private GraphNode goal;
private GraphNode start;
private List<GraphNode> path;
private List<GraphNode> origin;
public Graph()
{
    current = new GraphNode(0, 0);
    goal = new GraphNode(0, 0);
    start = new GraphNode(0, 0);
    path = new List<GraphNode>();
    origin = new List<GraphNode>();
}

方法setpath的定义:

public void SetPathing(int mouseX, int mouseY)
{
    if (Contains((int)mouseX / 32, (int)mouseY / 32))
    {
        goal = GetNode((int)mouseX / 32, (int)mouseY / 32);
        current = goal;
        path.Add(current);
        while ((current.X != start.X) && (current.X != start.X))
        {
            current = origin.Where(keyValuePair => (keyValuePair.Key.X == current.X) && (keyValuePair.Key.X == current.Y)).Select(keyValuePair => keyValuePair.Value).LastOrDefault();
            path.Add(current);
        }
    }
}

当我在setpath中的while循环开始时中断时，我在locals屏幕中看到以下信息:

current     null                    PathFinding.GraphNode
goal        {PathFinding.GraphNode} PathFinding.GraphNode
        X   0   int
        x   0   int
        Y   5   int
        y   5   int

在明确地将目标的参考值赋给当前之后，这怎么可能呢?

我可能错过了一些愚蠢的东西，但我找了两个小时也没有找到。这里没有异步操作

EDIT:我不想在我最初的问题上过于冗长，这里有一些额外的细节，我的道歉。下面是Contains, GetNode和GetNodeIndex的详细信息。没什么特别的，我是个业余爱好者。

    public int GetNodeIndex(int x, int y)
    {
        // Find the node index in the list based on x and y
        // Return -1 if not found
        return nodes.FindIndex(n => (n.X == x) && (n.Y == y));
    }
    public GraphNode GetNode(int x, int y)
    {
        // Find the node in the list based on x and y
        // Return null if not in list
        int nodeIndex = GetNodeIndex(x, y);
        if (nodeIndex != -1)
        {
            return nodes[nodeIndex];
        }
        return null;
    }
    public bool Contains(int x, int y)
    {
        // Check if the returned value is not -1
        if (GetNodeIndex(x, y) != -1)
        {
            return true;
        }
    }

这个用例实际上只是沿着下面的行:

using System;
namespace Graphs
{
    class Program 
    {
        static void Main() 
        {
            Graph graph = new Graph(20, 20);
            graph.SetPathing(Mouse.GetState().X, Mouse.GetState().Y);
        }
    }
}