title: NHibernate: Default value for a property over a null column
body: <p>I'm working with an old database used by other applications, so i can't modify its structure.
  Sometimes i have nullable columns that i want to map as a non nullable type.
  For instance I have a nullable EndValidity column on database which i want to map on a non nullable DateTime, and, if null, it should be DateTime.MaxValue, or as a more simple example, a nullable bit column that must be false if null.</p>
  
  <p>I'm thinking about writing a custom user type for it (with parameters if possible), or is it there something included in nHibernate for it?</p>
  
  <p>If the only solution is to write a custom usertype, for the boolean case, can I override fluentnhibernate conventions to always apply that usertype for booleans?</p>