How to unit test referenced property with nhibernate

What's the best practice if I'd like to unit test an entity with a referenced property?

BlogEntry is referencing a User object by a foreign key. Right now I'm using session.Load to avoid an exception since the foreign key cannot contain nulls.

Can i Mock this somehow instead? I don't want my unit test to contain references to a "real" user in the db.

 public class BlogEntry {
            public virtual int ID {get;set;}
            public virtual User CreatedBy {get;set;}
            public virtual string Text {get;set;}
        }

I'm currently using the following test method:

        [Test]
        public void Create_blog_entry()
        {
            using (var session = sessionFactory.OpenSession())
            using (var trans = session.BeginTransaction())
            {              
                var entry = new BlogEntry(){
                 Text = "Lorem ipsum",
                 CreatedBy = session.Load<User>(1)                 
                };

                session.Save(entry);
                trans.Rol开发者_StackOverflowlback();
            }
        }

[Test]
public void Create_blog_entry()
{
    using (var session = sessionFactory.OpenSession())
    using (var trans = session.BeginTransaction())
    {
        var user = new User { Id = 1 };
        session.Save(user);

        var entry = new BlogEntry()
        {
            Text = "Lorem ipsum",
            CreatedBy = user
        };

        session.Save(entry);
        trans.Rollback();
    }
}