Console.WriteLine(JsonSerializer.Serialize(object)); returning an empty object? [duplicate]

I am attempting to write the contents of an object to the console using Console.WriteLine(JsonSerializer.Serialize(object)); but it only writes a {} - which I assume is an empty JSON file?

Any help would be greatly appreciated.

namespace PetShopPart1
{

    public class Program
    {
        public static void Main(string[] args)
        {

            //DogLeash dogLeash = new DogLeash();
            //dogLeash.Quantity = 0;
            //dogLeash.Material = "0";
            //dogLeash.LengthInches = 0;


            DogLeash dogLeash = new DogLeash
            {
                Quantity = 1,
                Material = "0",
                LengthInches = 0,
            };
            
            string userInput = "0";

            while (userInput != "exit")
            {
        
                if (userInput == "1")
                {
                    Console.WriteLine("How many leashes would you like?\n");
                    dogLeash.Quantity = int.Parse(Console.ReadLine());
                    Console.WriteLine();
                    Console.WriteLine("What Material would you like your leash(es) to be made of.\n");
                    dogLeash.Material = Console.ReadLine();
                    Console.WriteLine();
                    Console.WriteLine("And how many inches would you like your leash to be?\n");
                    dogLeash.LengthInches = int.Parse(Console.ReadLine());
                    Console.WriteLine();

                    Console.WriteLine(JsonSerializer.Serialize(dogLeash));
                
                
                }

                Console.WriteLine("Press 1 to add an item.\n");
                Console.WriteLine("Type Exit to Quit.\n");
                userInput = Console.ReadLine();
            }

            
        }
    }
}

Dogleash.cs:

using System;

namespace PetShopPart1
{
    class DogLeash : Product
    {
        public int LengthInches;
        public string Material;
    }
}

Product.cs:

using System;
using System.ComponentModel;

namespace PetShopPart1
{
    public class Product
    {
        public string Name;
        public decimal Price;
        public int Quantity = 0;
        public string Description;
    }
}