fix(raidboss): Fixed RB Eilhalder von Hellmann not spawning

When the spawns were loaded during ig daytime, the night RB would not be added to the list of bosses managed by the DayNightSpawnManager.
This bug was introduced when the backing map for night bosses was moved to a ConcurrentHashMap, which does not support null values.
Changed the map implementation to a HashMap as concurrent access is highly unlikely, which allows to initialise the boss status with null.

src/main/java/com/l2jserver/gameserver/GameServer.java

@@ -336,7 +336,8 @@ public final class GameServer {
 		
 		printSection("Scripts");
 		ScriptEngineManager.getInstance().executeScriptList(new File(server().getDatapackRoot(), "data/scripts.cfg"));
-		
+
+		printSection("Spawns");
 		SpawnTable.getInstance().load();
 		DayNightSpawnManager.getInstance().trim().notifyChangeMode();
 		FourSepulchersManager.getInstance().init();

src/main/java/com/l2jserver/gameserver/instancemanager/DayNightSpawnManager.java

@@ -18,18 +18,17 @@
  */
 package com.l2jserver.gameserver.instancemanager;
 
-import java.util.ArrayList;
-import java.util.List;
-import java.util.Map;
-import java.util.concurrent.ConcurrentHashMap;
-
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-
 import com.l2jserver.gameserver.GameTimeController;
 import com.l2jserver.gameserver.model.L2Spawn;
 import com.l2jserver.gameserver.model.actor.L2Npc;
 import com.l2jserver.gameserver.model.actor.instance.L2RaidBossInstance;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
 
 /**
  * @author godson
@@ -42,9 +41,9 @@ public final class DayNightSpawnManager {
 	
 	private final List<L2Spawn> _nightCreatures = new ArrayList<>();
 	
-	private final Map<L2Spawn, L2RaidBossInstance> _bosses = new ConcurrentHashMap<>();
+	private final Map<L2Spawn, L2RaidBossInstance> _bosses = new HashMap<>();
 	
-	protected DayNightSpawnManager() {
+	private DayNightSpawnManager() {
 		// Prevent external initialization.
 	}
 	
@@ -165,7 +164,7 @@ public final class DayNightSpawnManager {
 				}
 				
 				if ((boss != null) && (boss.getId() == 25328) && boss.getRaidStatus().equals(RaidBossSpawnManager.StatusEnum.ALIVE)) {
-					handleHellmans(boss, mode);
+					handleHellmann(boss, mode);
 				}
 				return;
 			}
@@ -174,17 +173,17 @@ public final class DayNightSpawnManager {
 		}
 	}
 	
-	private void handleHellmans(L2RaidBossInstance boss, int mode) {
+	private void handleHellmann(L2RaidBossInstance boss, int mode) {
 		switch (mode) {
 			case 0 -> {
 				boss.deleteMe();
-				LOG.info("Deleting Hellman raidboss.");
+				LOG.info("Deleting Hellmann raidboss.");
 			}
 			case 1 -> {
 				if (!boss.isVisible()) {
 					boss.spawnMe();
 				}
-				LOG.info("Spawning Hellman raidboss.");
+				LOG.info("Spawning Hellmann raidboss.");
 			}
 		}
 	}
@@ -199,6 +198,8 @@ public final class DayNightSpawnManager {
 			_bosses.put(bossSpawn, raidboss);
 			
 			return raidboss;
+		} else {
+			_bosses.put(bossSpawn, null);
 		}
 		return null;
 	}