LS 3.0 Object reference not set to an instance of an object.

This looks like a bug in Lightspeed 3.0 build 13186.  Can you let me know if it can be fixed in a nightly build?
In Lightspeed 2.2 the following query worked but in Lightspeed 3.0 we get the following exception.

var query = (from gameHistory in uow.HistoryEntities
    where gameHistory.HistoryGame.ApplicationInstance.Id == appInstanceId
    orderby gameHistory.Id descending
    select gameHistory).FirstOrDefault();

  
Object reference not set to an instance of an object.

   at Mindscape.LightSpeed.Linq.Sqo.Where.WalkAndExtractAssociation(LinqQueryPlanExpression plan, Expression expression)
   at Mindscape.LightSpeed.Linq.Sqo.Where.ProcessCriteriaForRequiredJoins(QueryExpression criteria, LinqQueryPlanExpression plan, MethodCallExpression expression)
   at Mindscape.LightSpeed.Linq.Sqo.Where.ProcessCriteriaForRequiredJoins(QueryExpression criteria, LinqQueryPlanExpression plan, MethodCallExpression expression)
   at Mindscape.LightSpeed.Linq.Sqo.Where.Evaluate(ExpressionVisitor visitor, MethodCallExpression expression)
   at Mindscape.LightSpeed.Linq.Plan.LinqQueryBuilder.VisitMethodCall(MethodCallExpression exp)
   at Mindscape.LightSpeed.Linq.Plan.LinqQueryBuilder.Visit(Expression exp)
   at Mindscape.LightSpeed.Linq.Sqo.OrderSqo.Evaluate(ExpressionVisitor visitor, MethodCallExpression expression)
   at Mindscape.LightSpeed.Linq.Plan.LinqQueryBuilder.VisitMethodCall(MethodCallExpression exp)
   at Mindscape.LightSpeed.Linq.Plan.LinqQueryBuilder.Visit(Expression exp)
   at Mindscape.LightSpeed.Linq.Sqo.First.Evaluate(ExpressionVisitor visitor, MethodCallExpression expression)
   at Mindscape.LightSpeed.Linq.Plan.LinqQueryBuilder.VisitMethodCall(MethodCallExpression exp)
   at Mindscape.LightSpeed.Linq.Plan.LinqQueryBuilder.Visit(Expression exp)
   at Mindscape.LightSpeed.Linq.Plan.LinqQueryBuilder.Build(Expression translation, LinqQueryProvider provider)
   at Mindscape.LightSpeed.Linq.LinqQueryProvider.GetExecutionPlan(Expression expression)
   at Mindscape.LightSpeed.Linq.LinqQueryProvider.Execute(Expression expression)
   at Mindscape.LightSpeed.Linq.LinqQueryProvider.System.Linq.IQueryProvider.Execute[S](Expression expression)
   at System.Linq.Queryable.FirstOrDefault[TSource](IQueryable`1 source)
   at BlueYonder.Server.BusinessProcesses.ApplicationBP.FindLastApplicationTransactionId(Int64 appInstanceId)

If I change the query to the following then it works.
var query = (from gameHistory in uow.HistoryEntities
             where (gameHistory.HistoryGame != null) &&
                (gameHistory.HistoryGame.ApplicationInstance.Id == appInstanceId)
             orderby gameHistory.Id descending
             select gameHistory).FirstOrDefault();

We haven't been able to reproduce this error using our best guess at your class definitions, so I think we must be missing something about your entity classes or associations.  Could you provide us with a buildable repro sample please, including the relevant entity class definitions?  You can attach a zip file via the Options tab.  Thanks!