Błąd pluginu Mc_shop

[15:36:03 ERROR]: Could not pass event InventoryClickEvent to MC-SHOP v0.1.5
org.bukkit.event.EventException
        at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:310) ~[survival.jar:git-Spigot-d20369f-7fc5cd8]
        at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62) ~[survival.jar:git-Spigot-d20369f-7fc5cd8]
        at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:502) [survival.jar:git-Spigot-d20369f-7fc5cd8]
        at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:487) [survival.jar:git-Spigot-d20369f-7fc5cd8]
        at net.minecraft.server.v1_9_R1.PlayerConnection.a(PlayerConnection.java:1852) [survival.jar:git-Spigot-d20369f-7fc5cd8]
        at net.minecraft.server.v1_9_R1.PacketPlayInWindowClick.a(SourceFile:33) [survival.jar:git-Spigot-d20369f-7fc5cd8]
        at net.minecraft.server.v1_9_R1.PacketPlayInWindowClick.a(SourceFile:10) [survival.jar:git-Spigot-d20369f-7fc5cd8]
        at net.minecraft.server.v1_9_R1.PlayerConnectionUtils$1.run(SourceFile:13) [survival.jar:git-Spigot-d20369f-7fc5cd8]
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_121]
        at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_121]
        at net.minecraft.server.v1_9_R1.SystemUtils.a(SourceFile:45) [survival.jar:git-Spigot-d20369f-7fc5cd8]
        at net.minecraft.server.v1_9_R1.MinecraftServer.D(MinecraftServer.java:721) [survival.jar:git-Spigot-d20369f-7fc5cd8]
        at net.minecraft.server.v1_9_R1.DedicatedServer.D(DedicatedServer.java:400) [survival.jar:git-Spigot-d20369f-7fc5cd8]
        at net.minecraft.server.v1_9_R1.MinecraftServer.C(MinecraftServer.java:660) [survival.jar:git-Spigot-d20369f-7fc5cd8]
        at net.minecraft.server.v1_9_R1.MinecraftServer.run(MinecraftServer.java:559) [survival.jar:git-Spigot-d20369f-7fc5cd8]
        at java.lang.Thread.run(Thread.java:745) [?:1.8.0_121]
Caused by: java.lang.NullPointerException
        at pro.lvlup.mcshop.managers.GuiManager.getGuiItem(GuiManager.java:23) ~[?:?]
        at pro.lvlup.mcshop.listeners.InventoryListener.onClick(InventoryListener.java:35) ~[?:?]
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_121]
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_121]
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_121]
        at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_121]
        at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:306) ~[survival.jar:git-Spigot-d20369f-7fc5cd8]
        ... 15 more
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