无法强制转换类型为'；的对象；NHibernate.Hql.Ast.HqlBitwiseAnd'；键入

我有下面的代码段，在其中我得到了错误

using (var session = Database.OpenSession())
{
    var q = from x in session.Query<User>()
           where x.UserName == username & x.Password==EncodePassword(password)
            select x;
    if (q.Count() > 0)
     {
         result = true;
     }
}

在if语句上，我收到错误

Unable to cast object of type 'NHibernate.Hql.Ast.HqlBitwiseAnd' to type 'NHibernate.Hql.Ast.HqlBooleanExpression'.

using (var session = Database.OpenSession())
{
    var q = from x in session.Query<User>()
           where x.UserName == username && x.Password==EncodePassword(password)
            select x;
    if (q.Count() > 0)
     {
         result = true;
     }
}