gcserror

[Craft Scheduler Thread - 686/WARN]: Exception in thread "Craft Scheduler Thread - 686"
[21:18:25] [Craft Scheduler Thread - 686/WARN]: org.apache.commons.lang.UnhandledException: Plugin GlobalChestShop v1.2.050 generated an exception while executing task 54895312
	at org.bukkit.craftbukkit.v1_8_R3.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:56)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
	at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NullPointerException: null value in entry: skull-owner=null
	at com.google.common.collect.CollectPreconditions.checkEntryNotNull(CollectPreconditions.java:33)
	at com.google.common.collect.ImmutableMap.entryOf(ImmutableMap.java:135)
	at com.google.common.collect.ImmutableMap$Builder.put(ImmutableMap.java:206)
	at org.bukkit.craftbukkit.v1_8_R3.inventory.CraftMetaSkull.serialize(CraftMetaSkull.java:173)
	at org.bukkit.craftbukkit.v1_8_R3.inventory.CraftMetaItem.serialize(CraftMetaItem.java:850)
	at org.bukkit.craftbukkit.v1_8_R3.inventory.CraftMetaItem.toString(CraftMetaItem.java:961)
	at java.lang.String.valueOf(String.java:2981)
	at java.lang.StringBuilder.append(StringBuilder.java:131)
	at org.bukkit.inventory.ItemStack.toString(ItemStack.java:304)
	at eu.blockup.GlobalChestShop.Util.ItemControler.serializeItemStack(ItemControler.java:335)
	at eu.blockup.GlobalChestShop.Util.ItemControler.getInteralIdOfItemStack(ItemControler.java:168)
	at eu.blockup.GlobalChestShop.Util.GUI.GUI_CustomCategoryAddItem$2.onButtonClick(GUI_CustomCategoryAddItem.java:89)
	at eu.blockup.GlobalChestShop.Util.GUI.Core.Buttons.Button.onPreButtonClick(Button.java:69)
	at eu.blockup.GlobalChestShop.Util.GUI.Core.Core.EventListener$2.run(EventListener.java:211)
	at org.bukkit.craftbukkit.v1_8_R3.scheduler.CraftTask.run(CraftTask.java:71)
	at org.bukkit.craftbukkit.v1_8_R3.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:53)
	... 3 more