Ambiguous UrlExtensions.ToUrl method behaviour

UrlExtensionsTest.cs

[Route("/route/{Id}")]
public class JustId : IReturn
{
    public long Id { get; set; }
}

[Route("route/{Id}")]
public class JustId_NoSlash : IReturn
{
    public long Id { get; set; }
}

[TestFixture]
public class UrlExtensionTests
{
  [Test]
  public void Starting_slash_test_Fails()
  {
      var serviceEndpoint = new Uri("http://localhost/api/", UriKind.Absolute);
      var actionUrl = new Uri(new JustId { Id = 1 }.ToUrl("GET"), UriKind.Relative);
      
      Assert.That(new Uri(serviceEndpoint, actionUrl).ToString(), Is.EqualTo("http://localhost/api/route/1"));
  }

  [Test]
  public void Starting_slash_test_Passes()
  {
      var serviceEndpoint = new Uri("http://localhost/api/", UriKind.Absolute);
      var actionUrl = new Uri(new JustId_NoSlash { Id = 1 }.ToUrl("GET"), UriKind.Relative);

      Assert.That(new Uri(serviceEndpoint, actionUrl).ToString(), Is.EqualTo("http://localhost/api/route/1"));
  }
}