New family instance on the reference plane

[Transaction(TransactionMode.Manual)]
    public class Command : IExternalCommand
    {
        public Result Execute(
          ExternalCommandData commandData,
          ref string message,
          ElementSet elements)
        {
            UIApplication uiapp = commandData.Application;
            UIDocument uidoc = uiapp.ActiveUIDocument;
            Application app = uiapp.Application;
            Document doc = uidoc.Document;

            Reference r;

            try
            {
                r = uidoc.Selection.PickObject(ObjectType.Element, new ReferencePlaneSelectionFilter());
            }
            catch (OperationCanceledException)
            {
                return Result.Cancelled;
            }





            var referencePlane = doc.GetElement(r.ElementId) as ReferencePlane;


            FilteredElementCollector collector =
                new FilteredElementCollector(doc);

            var familySymbol =
                collector
                    .OfClass(typeof (FamilySymbol))
                    .FirstOrDefault(fs => fs.Name.Equals("Семейство на основе грани")) as FamilySymbol;

            using (var t = new Transaction(doc, "Вставка семейства"))
            {
                t.Start();


                for (double x = -1; x <= 1; x += 1)
                {
                    for (double y = -1; y <= 1; y += 1)
                    {
                        for (double z = -1; z <= 1; z += 1)
                        {


                            XYZ direction = new XYZ(x, y, z);
                            Debug.Print("X: {0}; Y: {1}; Z: {2}", direction.X, direction.Y, direction.Z);


                            FamilyInstance createdFamilyInstance =
                                CreateFamilyInstanceOnReference(doc, referencePlane.Reference, referencePlane.Plane.Origin, direction, familySymbol);

                            if (createdFamilyInstance != null)
                            {
                                Debug.Print(direction.ToString());
                            }
                        }
                    }
                }


                //var fs1 = doc.Create.NewFamilyInstance(XYZ.Zero, familySymbol, new XYZ(0,0,1), referencePlane,
                //    StructuralType.NonStructural);

                //var fs = doc.Create.NewFamilyInstance(referencePlane.Reference,
                //    XYZ.Zero, referencePlane.Normal,
                //    familySymbol);


                t.Commit();
            }
            return Result.Succeeded;
        }

        FamilyInstance CreateFamilyInstanceOnReference(Document doc, Reference r, XYZ position, XYZ direction, FamilySymbol fs)
        {
            try
            {
                return doc.Create.NewFamilyInstance(r, position, direction, fs);
            }
            catch (Exception ex)
            {
                //Debug.Print(ex.Message);
                return null;

            }
        }
    }

    public class ReferencePlaneSelectionFilter : ISelectionFilter
    {
        public bool AllowElement(Element elem)
        {
            return elem is ReferencePlane;
        }

        public bool AllowReference(Reference reference, XYZ position)
        {
            throw new NotImplementedException();
        }
    }