LINQ to SQL NullReferenceException gotcha

In my DAL (Data Access Layer) assembly (a LINQ-to-SQL centric assembly) I used to insert object into the database like this public void CreateMessage(MyApp.Entities.Message message) { Message m = new Message(); // this is the LINQ-to-SQL generated Message class not the business entity class m.UserId = message.UserId; //... set all the properties accordingly DataContext ctx = new DataCo...