I have a problem with NHibernate, I can't seem to find any solution for.
In my project I have a simple entity (Batch), but whenever I try and run the following test, I get an exception.
I've triede a couple of different ways to perform a similar query, but almost identical exception for all (it differs in which LINQ method being executed).

The first test:

```
[Test]
public void QueryLatestBatch()
{
    using (var session = SessionManager.OpenSession())
    {
        var batch = session.Query<Batch>()
            .FirstOrDefault();

        Assert.That(batch, Is.Not.Null);
    }
}

```

The exception:

```
System.NullReferenceException : Object reference not set to an instance of an object.
at NHibernate.Linq.NhQueryProvider.PrepareQuery(Expression expression, ref IQuery query, ref NhLinqExpression nhQuery)
at NHibernate.Linq.NhQueryProvider.Execute(Expression expression)
at System.Linq.Queryable.FirstOrDefault(IQueryable`1 source)

```

The second test:

```
[Test]
public void QueryLatestBatch2()
{
    using (var session = SessionManager.OpenSession())
    {
        var batch = session.Query<Batch>()
            .OrderBy(x => x.Executed)
            .Take(1)
            .SingleOrDefault();

        Assert.That(batch, Is.Not.Null);
    }
}

```

The exception:

```
System.NullReferenceException : Object reference not set to an instance of an object.
at NHibernate.Linq.NhQueryProvider.PrepareQuery(Expression expression, ref IQuery query, ref NhLinqExpression nhQuery)
at NHibernate.Linq.NhQueryProvider.Execute(Expression expression)
at System.Linq.Queryable.SingleOrDefault(IQueryable`1 source)

```

However, this one is passing (using QueryOver<>):

```
[Test]
public void QueryOverLatestBatch()
{
    using (var session = SessionManager.OpenSession())
    {
        var batch = session.QueryOver<Batch>()
            .OrderBy(x => x.Executed).Asc
            .Take(1)
            .SingleOrDefault();

        Assert.That(batch, Is.Not.Null);
        Assert.That(batch.Executed, Is.LessThan(DateTime.Now));
    }
}

```

Using the QueryOver<> API is not bad at all, but I'm just kind of baffled that the Query<> API isn't working, which is kind of sad, since the First() operation is very concise, and our developers really enjoy LINQ.

I really hope there is a solution to this, as it seems strange if these methods are failing such a simple test.

**EDIT**

I'm using Oracle 11g, my mappings are done with FluentNHibernate registered through Castle Windsor with the NHibernate Facility.
As I wrote, the odd thing is that the query works perfectly with the QueryOver<> API, but not through LINQ.