.NET Core Deserialize from JSON file [duplicate]

I want to read a json file and parse it to C# attributes, but I got some errors like this

Unhandled exception. System.NullReferenceException: Object reference not set to an instance of an object.

This is my code:

public class Program
{
    public static void Main(string[] args)
    {
        Item item = FileReader.Read<Item>("Levels/Level1.json");
        foreach (string command in item.commands)
        {
            Console.WriteLine(command);
        }
    }
}

public class Item 
{
     public string controlable;
     public List<string> commands;
     public List<Object> objects;
     public struct Object
     {
         public string symbol;
         public ObjectPosition position;
     }
     public struct ObjectPosition
     {
         public int x;
         public int y;
     } 
}

using System.Text.Json;

public class FileReader
{
    public static T Read<T>(string fileName)
    {
        string text = File.ReadAllText(fileName);
        return JsonSerializer.Deserialize<T>(text);
    }
}

{
    "controlable": "R",
    "commands": ["Forward", "Backward"],
    "objects": [
        {
            "symbol": "B",
            "position": {
                "x": 3,
                "y": 5
            }
        }
    ]
}

The attributes not set from json file, is it error coz I don't use asyncronous? how to fix it?