Hey I get this error everytime the class changer popup happens in my server and it says null and don't show anything.

[18:14:48] ERROR Quest Error!
java.lang.NullPointerException
        at l2ro.gameserver.cache.ImagesCache.sendUsedImages(ImagesCache.java:225)
        at l2ro.gameserver.model.quest.QuestState.showTutorialHTML(QuestState.java:837)
        at quests._255_Tutorial.checkClassMaster(_255_Tutorial.java:1476)
        at quests._255_Tutorial.onEvent(_255_Tutorial.java:455)
        at l2ro.gameserver.model.quest.Quest.notifyEvent(Quest.java:604)
        at l2ro.gameserver.model.Player.processQuestEvent(Player.java:1468)
        at l2ro.gameserver.network.clientpackets.RequestTutorialPassCmdToServer.runImpl(RequestTutorialPassCmdToServer.java:94)
        at l2ro.gameserver.network.clientpackets.L2GameClientPacket.run(L2GameClientPacket.java:49)
        at l2ro.commons.net.nio.impl.MMOExecutableQueue.run(MMOExecutableQueue.java:39)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at java.lang.Thread.run(Unknown Source)

the cache try to show images, images missing?

Thanks yes I deleted the image and put another one in there but I renamed the link for the image to link to the new one and this is what I get it is the turtorial.java file in quest.

originally cache dont work like that

How does cache work is there something that im missing so it can read the new tutorial.java edited with my server info because when the class change pops up it shows this.