...

Services/Immortal/BuildOrderService.cs

@@ -282,7 +282,8 @@ public class BuildOrderService : IBuildOrderService
     {
         return (from ordersAtTime in _buildOrder.StartedOrders
             from orders in ordersAtTime.Value
-            where ordersAtTime.Key + (orders.Production() == null ? 0 : orders.Production().BuildTime) <= interval
+            let production = orders.Production()
+            where ordersAtTime.Key + (production?.BuildTime ?? 0) <= interval
             select orders).ToList();
     }