src/de/steamwar/lobby/listener/RabbitListener.java

@@ -42,6 +42,9 @@ public class RabbitListener implements Listener {
         World world = Bukkit.getWorlds().get(0);
         spreadRabbits(250, world);
         Bukkit.getScheduler().runTaskTimer(LobbySystem.getInstance(), () -> {
+            if(Bukkit.getOnlinePlayers().isEmpty()) {
+                return;
+            }
             Rabbit rabbit = world.getEntitiesByClass(Rabbit.class).iterator().next();
             world.spawn(rabbit.getLocation(), Firework.class, firework -> {
                 FireworkMeta meta = firework.getFireworkMeta();