fix: null-safe upgradeDateTime conversion in BuildingManager.setUpgradeDateTime

Placing a banestone (and other callers) pass null to clear a fresh
building's upgrade timer, but the inline .atZone(...).toInstant() NPE'd
on null. Convert only when non-null; the DB layer already handles null.

src/engine/gameManager/BuildingManager.java

@@ -25,6 +25,7 @@ import engine.objects.*;
 import engine.server.MBServerStatics;
 import org.pmw.tinylog.Logger;
 
+import java.time.Instant;
 import java.time.LocalDateTime;
 import java.time.ZoneId;
 import java.util.ArrayList;
@@ -274,7 +275,8 @@ public enum BuildingManager {
 
         if (building == null)
             return;
-        if (!DbManager.BuildingQueries.updateBuildingUpgradeTime(upgradeDateTime.atZone(ZoneId.systemDefault()).toInstant(), building, rankCost)) {
+        Instant instant = (upgradeDateTime == null) ? null : upgradeDateTime.atZone(ZoneId.systemDefault()).toInstant();
+        if (!DbManager.BuildingQueries.updateBuildingUpgradeTime(instant, building, rankCost)) {
             Logger.error("Failed to set upgradeTime for building " + building.getObjectUUID());
             return;
         }

src/engine/net/client/msg/ArcMineWindowAvailableTimeMsg.java

@@ -17,9 +17,8 @@ import engine.net.Protocol;
 import engine.objects.Building;
 import engine.objects.Guild;
 import engine.server.MBServerStatics;
-import java.time.Instant;
+import java.time.LocalDateTime;
 import java.time.Duration;
-import java.time.temporal.ChronoField;
 
 public class ArcMineWindowAvailableTimeMsg extends ClientNetMsg {
 
@@ -28,7 +27,7 @@ public class ArcMineWindowAvailableTimeMsg extends ClientNetMsg {
 
     private int currentMineHour;
     private Duration secondsLeft;
-    private Instant lateTime;
+    private LocalDateTime lateTime;
     private int late;
 
     /**
@@ -73,15 +72,15 @@ public class ArcMineWindowAvailableTimeMsg extends ClientNetMsg {
             currentMineHour = guild.getMineTime();
 
         late = MBServerStatics.MINE_LATE_WINDOW;
-        lateTime = Instant.now();
+        lateTime = LocalDateTime.now();
 
         if (late == 0)
-            lateTime = lateTime.plus(Duration.ofDays(1));
+            lateTime = lateTime.plusDays(1);
 
-        lateTime = lateTime.with(ChronoField.HOUR_OF_DAY, late);
+        lateTime = lateTime.withHour(late);
 
         late = ((late > 23) ? (late - 24) : late);
-        secondsLeft = Duration.between(Instant.now(), lateTime);
+        secondsLeft = Duration.between(LocalDateTime.now(), lateTime);
     }
 
     /**