Enum value not serialized

[redrabbit007]

I have an enum, and a class that contains an enum property:

namespace TomlynTests
{
  public enum SizeType : byte
  {
    Average,
    Big,
    Small
  }
}

namespace TomlynTests
{
  public class TestModel
  {
    public string Name { get; set; }

    public SizeType Size { get; set; }

    public TestModel(string name, SizeType size)
    {
      Name = name;
      Size = size;
    }
  }
}

When I create toml text from this the enum property value isn't serialized:

using Tomlyn.Model;
using Tomlyn;
using TomlynTests;

TestModel model = new("Pliers", SizeType.Small);

TomlTable table = new()
{
  { "model", model }
};

string text = Toml.FromModel(table);
Console.WriteLine(text);

[model]
name = "Pliers"
[model.size]

Is there something special I need to do to serialize enums?