Question: why List<int> property causes error: object containing type(s) must be partial?

using System;
using System.Collections.Generic;
using MemoryPack;

public class Program
{
	public static void Main()
	{
		var person = new Person();
		var bin = MemoryPackSerializer.Serialize(person);
	}

	[MemoryPackable]
	public partial class Person
	{
		public  List<int> IntItems { get; set; }
		public List<string> StringItems { get; set; }
	}
}

error MEMPACK042: The MemoryPackable object 'Person' containing type(s) must be partial

the docs says int, string, List<> are supported

Start with the minimal C# reproduction in the issue and reproduce diagnostic MEMPACK042 for the MemoryPackable Person containing List and List properties. Trace the diagnostic's handling of these property types and compare it with the documented supported types; done means the behavior or its explanation is consistent with the docs.