protected override void ProcessAspect(ClassAspect aspect, int currentSlot, bool isNull
                                       )
 {
     if (isNull)
     {
         if (aspect is FieldMetadata)
         {
             FieldMetadata field = (FieldMetadata)aspect;
             field.RemoveIndexEntry(context.Transaction(), context.ObjectId(), null);
         }
         return;
     }
     aspect.Delete(context, isUpdate);
 }