Validation failing when it should pass: .Empty()/.When()

I am trying to understand why my validation test is failing, when I expect it to pass.

Here is the code:

using FluentValidation;

namespace FluentValidationIssue
{
    public class Model
    {
        public string Ean { get; set; }
        internal List<string>? ProvidedEans { get; private set; }
        internal string? SelectedSourceSetId { get; set; }
        internal string? SetName { get; set; }
    }

    public class ModelValidator : AbstractValidator<Model>
    {
        public ModelValidator()
        {
            RuleFor(model => model.SetName).NotEmpty();

            // nothing provided
            RuleFor(model => model.SelectedSourceSetId)
                .Empty()
            .When(model => model.ProvidedEans is null || model.ProvidedEans!.Count == 0)
            .WithMessage("Either an existing override/ymal set or a list of Eans must be provided.");

            // both an existing and a list provided.
            RuleFor(model => model.SelectedSourceSetId)
                .NotEmpty()
                .When(model => model?.ProvidedEans?.Count > 0)
                .WithMessage("Choose either an existing override/ymal set or provide a list of Eans, not both.");
        }
    }

    /// <summary> A program. </summary>
    internal class Program
    {
        /// <summary> Main entry-point for this application. </summary>
        static void Main(string[] args)
        {
            var model = new Model
            {
                Ean = "9780316587266",
                WorkId = 1234,
                SetName = "Set Name 1"
                SelectedSourceSetId = "a59ea6d32f6444c8afef284e557ab319"
            };

            var validator = new ModelValidator();
            var result = validator.Validate(model);
            if (result.IsValid)
            {
                Console.WriteLine("The model is valid.");
            }
            else
            {
                Console.WriteLine("The model is invalid.");
                foreach (var error in result.Errors)
                {
                    Console.WriteLine($"- {error.PropertyName}: {error.ErrorMessage}");
                }
            }
        }
    }
}

Given that I populated the model.SelectedSourceSetId with a string value, I expect the first rule to pass. Except it is failing and returns my custom message.

If I leave model.SelectedSourceSetId set to null, the first rule passes, and it should fail.

If I provide values for both SelectedSourceSetId and ProvidedEans, the second rule passes, when it should fail.

I am trying to do a cross field check. The model needs to have either a SelectedSourceSetId or a list of strings (ProvidedEans), but not both.

The rules are:

1. If SelectedSourceSetId is an empty string/null and the ProvidedEans is null or ProvidedEans is an empty collection (Count == 0), than the error message should be triggered.

2. If SelectedSourceSetId is an not empty/null and the ProvidedEans contains at least one item, than the error message should be triggered.