Запрос свойства байта с nhibernate вызывает недопустимую ошибку приведения

Есть ли проблема с nhibernate 3.1.0.4000, где запрашивается свойство байта:

byte code = 2;
Group g = Repository<Group>.FindOne(p => p.Code == code);

Текст исключения:

Cause 'Specified cast is not valid.'

[InvalidCastException: Specified cast is not valid.]
   NHibernate.Type.ByteType.Set(IDbCommand cmd, Object value, Int32 index) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Type\ByteType.cs:44
   NHibernate.Type.NullableType.NullSafeSet(IDbCommand cmd, Object value, Int32 index) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Type\NullableType.cs:180
...

[GenericADOException: could not execute query
[ select group0_.LabourLawGroupId as LabourLa1_235_, group0_.Code as Code235_ from personnel.LabourLawGroup group0_ where group0_.Code=? ]
  Name:p1 - Value:4
[SQL: select group0_.LabourLawGroupId as LabourLa1_235_, group0_.Code as Code235_ from personnel.LabourLawGroup group0_ where group0_.Code=?]]
   NHibernate.Loader.Loader.DoList(ISessionImplementor session, QueryParameters queryParameters) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Loader\Loader.cs:1703
   NHibernate.Loader.Loader.ListIgnoreQueryCache(ISessionImplementor session, QueryParameters queryParameters) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Loader\Loader.cs:1601
   NHibernate.Loader.Loader.List(ISessionImplementor session, QueryParameters queryParameters, ISet`1 querySpaces, IType[] resultTypes) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Loader\Loader.cs:1591
   NHibernate.Hql.Ast.ANTLR.Loader.QueryLoader.List(ISessionImplementor session, QueryParameters queryParameters) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Hql\Ast\ANTLR\Loader\QueryLoader.cs:300
   NHibernate.Hql.Ast.ANTLR.QueryTranslatorImpl.List(ISessionImplementor session, QueryParameters queryParameters) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Hql\Ast\ANTLR\QueryTranslatorImpl.cs:108
   NHibernate.Engine.Query.HQLQueryPlan.PerformList(QueryParameters queryParameters, ISessionImplementor session, IList results) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Engine\Query\HQLQueryPlan.cs:78
   NHibernate.Impl.SessionImpl.List(IQueryExpression queryExpression, QueryParameters queryParameters, IList results) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Impl\SessionImpl.cs:645
   NHibernate.Impl.AbstractSessionImpl.List(IQueryExpression queryExpression, QueryParameters parameters) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Impl\AbstractSessionImpl.cs:92
   NHibernate.Impl.ExpressionQueryImpl.List() in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Impl\ExpressionQueryImpl.cs:60
   NHibernate.Linq.NhQueryProvider.ExecuteQuery(NhLinqExpression nhLinqExpression, IQuery query, NhLinqExpression nhQuery) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Linq\NhQueryProvider.cs:79
   NHibernate.Linq.NhQueryProvider.Execute(Expression expression) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Linq\NhQueryProvider.cs:103
   System.Linq.Queryable.SingleOrDefault(IQueryable`1 source) +265
   Azarakhsh.Framework.Repository.NHibernateRepository`1.FindOne(Expression`1 expression) +223
   Azarakhsh.Framework.Repository.Repository`1.FindOne(Expression`1 expression) +100