public void EliminarTelefonoNull()
{
Alumno alumno = new AlumnoLocal(Legajo.Of("123"), "Lisandro", "Martinez", new DateTime(2019, 1, 1));
var telefono = new Telefono("011", "48603242");
alumno.AgregarTelefono(telefono);
alumno.Telefonos.Should().Contain(telefono).And.HaveCount(1);
alumno = null;
telefono.Should().BeNull();
}