总是返回 null 的方法

Question

I'm stuck with a piece of a code I'm translating from Java to C#.

Basically, I have a Map(Dictionary) with keys composed by Pair and Values represented by a class made by me (Square); in this class there's only one field, which is Optional (yes, I create the Optional class in C#).

At the beginning I fill this Dictionary with pairs to make a simil-grid and empty Optional, as you can see in the code below.

class World
{
    private Dictionary<Pair<int, int>, Square> map = 
        new Dictionary<Pair<int, int>, Square>();

    public World(int width, int height)
    {
        this.size = new Pair<int, int>(width, height);
        for (int w = 0; w < this.size.GetX(); w++)
        {
            for (int h = 0; h < this.size.GetY(); h++)
                this.map.Add(new Pair<int, int>(w, h), 
                    new Square(Optional<Entity>.Empty()));
        }
    }
}

And this is the Square class

class Square
{
    private Optional<Entity> entity;

    public Square (Optional<Entity> entity)
    {
        this.entity = entity;
    }

    public Optional<Entity> GetEntity() 
    {
        return this.entity;
    }

    public void SetEntity(Optional<Entity> entity)
    {
        this.entity = entity;
    }
}

Here's the problem, this function below always returns null when I try to get an existent value from the Dictionary, it throws System.NullReferenceException: Object reference not set to an instance of an object. In this code I cut away all the controls, but I know that I try to get a value already inserted; also, I tried to run Dictionary.ContainsValue and it return false. But I do have inizialed the Dictionary.

public Square? GetSquare(int x, int y)
{
    if (y < this.size.GetY() && y >= 0 && < x this.size.GetX() && x >= 0)
    {
        this.map.TryGetValue(new Pair<int, int>(x, y), out Square? square);
        return square;
    }

    throw new InvalidOperationException("no square in this position!");
}

I leave here the code of the Optional class too, but I'm almost 100% sure that it's not the problem

public class Optional<T>
{
    private T value;
    public bool IsPresent { get; set; } = false;

    private Optional() { }

    public static Optional<T> Empty()
    {
        return new Optional<T>();
    }

    public static Optional<T> Of(T value)
    {
        Optional<T> obj = new Optional<T>();
        obj.Set(value);
        return obj;
    }

    private void Set(T value)
    {
        this.value = value;
        this.IsPresent = true;
    }

    public T Get()
    {
        return value;
    }
}

This is Pair class

    public class Pair<X, Y>
    {
        private X first;
        private Y second;

        public Pair(X first, Y second)
        {
            this.first = first;
            this.second = second;
        }
        public X GetX()
        {
            return this.first;
        }

        public Y GetY()
        {
            return this.second;
        }

        public override string ToString()
        {
            return "<" + first + "," + second + ">";
        }
    }

Answer 1

Ok, solved it. The problem was, as you said, the Pair class. I substitute it with the ValueTuple<> class and now everything works fine, still thanks.