Error message

Could not pass event InventoryClickEvent to GUIShop v6.1.5
org.bukkit.event.EventException: null
        at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:306) ~[spigot.jar:git-Spigot-b78586d-753a8e7]
        at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62) ~[spigot.jar:git-Spigot-b78586d-753a8e7]
        at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:499) [spigot.jar:git-Spigot-b78586d-753a8e7]
        at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:484) [spigot.jar:git-Spigot-b78586d-753a8e7]
        at net.minecraft.server.v1_12_R1.PlayerConnection.a(PlayerConnection.java:1877) [spigot.jar:git-Spigot-b78586d-753a8e7]
        at net.minecraft.server.v1_12_R1.PacketPlayInWindowClick.a(SourceFile:33) [spigot.jar:git-Spigot-b78586d-753a8e7]
        at net.minecraft.server.v1_12_R1.PacketPlayInWindowClick.a(SourceFile:10) [spigot.jar:git-Spigot-b78586d-753a8e7]
        at net.minecraft.server.v1_12_R1.PlayerConnectionUtils$1.run(SourceFile:13) [spigot.jar:git-Spigot-b78586d-753a8e7]
        at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) [?:1.8.0_101]
        at java.util.concurrent.FutureTask.run(Unknown Source) [?:1.8.0_101]
        at net.minecraft.server.v1_12_R1.SystemUtils.a(SourceFile:46) [spigot.jar:git-Spigot-b78586d-753a8e7]
        at net.minecraft.server.v1_12_R1.MinecraftServer.D(MinecraftServer.java:747) [spigot.jar:git-Spigot-b78586d-753a8e7]
        at net.minecraft.server.v1_12_R1.DedicatedServer.D(DedicatedServer.java:405) [spigot.jar:git-Spigot-b78586d-753a8e7]
        at net.minecraft.server.v1_12_R1.MinecraftServer.C(MinecraftServer.java:678) [spigot.jar:git-Spigot-b78586d-753a8e7]
        at net.minecraft.server.v1_12_R1.MinecraftServer.run(MinecraftServer.java:576) [spigot.jar:git-Spigot-b78586d-753a8e7]
        at java.lang.Thread.run(Unknown Source) [?:1.8.0_101]
Caused by: java.lang.NullPointerException
        at org.bukkit.craftbukkit.v1_12_R1.entity.CraftHumanEntity.openInventory(CraftHumanEntity.java:186) ~[spigot.jar:git-Spigot-b78586d-753a8e7]
        at com.pablo67340.shop.handler.Shop.open(Shop.java:328) ~[?:?]
        at com.pablo67340.shop.listener.PlayerListener.onShopClick(PlayerListener.java:231) ~[?:?]
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_101]
        at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_101]
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_101]
        at java.lang.reflect.Method.invoke(Unknown Source) ~[?:1.8.0_101]
        at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:302) ~[spigot.jar:git-Spigot-b78586d-753a8e7]
        ... 15 more