Config generator overwrites existing properties when provided with empty config section #91380

using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Hosting;

namespace ConfigBindRepro
{
    internal class Program
    {
        static void Main()
        {
            HostApplicationBuilder builder = Host.CreateEmptyApplicationBuilder(settings: null);
            builder.Configuration.AddInMemoryCollection(new KeyValuePair<string, string?>[]
            {
                 new("A:B:ConnectionString", "localhost"),
            });

            AClass instance = new();
            builder.Configuration.GetSection("A:B").Bind(instance); // sets ConnectionString to "localhost"
            builder.Configuration.GetSection("A").Bind(instance); // source gen: sets ConnectionString to null, reflection: does not change the value

            Console.WriteLine($"The value is '{instance.ConnectionString}'");
        }
    }

    public class AClass
    {
        public string? ConnectionString { get; set; }
    }
}