Is null a valid value for a dependency from a factory method?

Program.cs

namespace ConsoleApplication1
{
	using Castle.MicroKernel.Registration;
	using Castle.Windsor;
	using Castle.Windsor.Installer;

	public interface IFoo
	{
	}

	public class Foo : IFoo
	{
		public static IFoo CreateFoo()
		{
			return null;
		}
	}

	public interface IBar
	{
	}

	public class Bar : IBar
	{
		private readonly IFoo foo;

		public Bar(IFoo foo = null)
		{
			this.foo = foo;
		}
	}

	class Program
	{
		private static IWindsorContainer _container;

		static void Main(string[] args)
		{
			_container = new WindsorContainer().Install(FromAssembly.This());
			_container.Register(Component.For<IFoo>().UsingFactoryMethod(Foo.CreateFoo));
			_container.Register(Component.For<IBar>().ImplementedBy<Bar>());

			var service = _container.Resolve<IBar>();
		}
	}
}