GUI Error

[15:45:29] [Server thread/ERROR]: Could not pass event PlayerInteractEvent to GalaxyEnchants va1.0
org.bukkit.event.EventException: null
        at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:320) ~[spigot-1.14.4.jar:git-Spigot-56f8471-ccd47a5]
        at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:70) ~[spigot-1.14.4.jar:git-Spigot-56f8471-ccd47a5]
        at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:529) ~[spigot-1.14.4.jar:git-Spigot-56f8471-ccd47a5]
        at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:514) ~[spigot-1.14.4.jar:git-Spigot-56f8471-ccd47a5]
        at org.bukkit.craftbukkit.v1_14_R1.event.CraftEventFactory.callPlayerInteractEvent(CraftEventFactory.java:437) ~[spigot-1.14.4.jar:git-Spigot-56f8471-ccd47a5]
        at org.bukkit.craftbukkit.v1_14_R1.event.CraftEventFactory.callPlayerInteractEvent(CraftEventFactory.java:404) ~[spigot-1.14.4.jar:git-Spigot-56f8471-ccd47a5]
        at org.bukkit.craftbukkit.v1_14_R1.event.CraftEventFactory.callPlayerInteractEvent(CraftEventFactory.java:400) ~[spigot-1.14.4.jar:git-Spigot-56f8471-ccd47a5]
        at net.minecraft.server.v1_14_R1.PlayerConnection.a(PlayerConnection.java:1277) ~[?:git-Spigot-56f8471-ccd47a5]
        at net.minecraft.server.v1_14_R1.PacketPlayInBlockPlace.a(PacketPlayInBlockPlace.java:28) ~[spigot-1.14.4.jar:git-Spigot-56f8471-ccd47a5]
        at net.minecraft.server.v1_14_R1.PacketPlayInBlockPlace.a(PacketPlayInBlockPlace.java:1) ~[spigot-1.14.4.jar:git-Spigot-56f8471-ccd47a5]
        at net.minecraft.server.v1_14_R1.PlayerConnectionUtils.lambda$0(PlayerConnectionUtils.java:19) ~[spigot-1.14.4.jar:git-Spigot-56f8471-ccd47a5]
        at net.minecraft.server.v1_14_R1.TickTask.run(SourceFile:18) [spigot-1.14.4.jar:git-Spigot-56f8471-ccd47a5]
        at net.minecraft.server.v1_14_R1.IAsyncTaskHandler.executeTask(SourceFile:144) [spigot-1.14.4.jar:git-Spigot-56f8471-ccd47a5]
        at net.minecraft.server.v1_14_R1.IAsyncTaskHandlerReentrant.executeTask(SourceFile:23) [spigot-1.14.4.jar:git-Spigot-56f8471-ccd47a5]
        at net.minecraft.server.v1_14_R1.IAsyncTaskHandler.executeNext(SourceFile:118) [spigot-1.14.4.jar:git-Spigot-56f8471-ccd47a5]
        at net.minecraft.server.v1_14_R1.MinecraftServer.aX(MinecraftServer.java:909) [spigot-1.14.4.jar:git-Spigot-56f8471-ccd47a5]
        at net.minecraft.server.v1_14_R1.MinecraftServer.executeNext(MinecraftServer.java:902) [spigot-1.14.4.jar:git-Spigot-56f8471-ccd47a5]
        at net.minecraft.server.v1_14_R1.IAsyncTaskHandler.awaitTasks(SourceFile:127) [spigot-1.14.4.jar:git-Spigot-56f8471-ccd47a5]
        at net.minecraft.server.v1_14_R1.MinecraftServer.sleepForTick(MinecraftServer.java:886) [spigot-1.14.4.jar:git-Spigot-56f8471-ccd47a5]
        at net.minecraft.server.v1_14_R1.MinecraftServer.run(MinecraftServer.java:819) [spigot-1.14.4.jar:git-Spigot-56f8471-ccd47a5]
        at java.lang.Thread.run(Thread.java:834) [?:?]
Caused by: java.lang.NullPointerException
        at java.lang.String.contains(String.java:2036) ~[?:?]
        at me.zaxos.galaxyenchants.InventoryHandler.onDo(InventoryHandler.java:396) ~[?:?]
        at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:?]
        at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:?]
        at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:?]
        at java.lang.reflect.Method.invoke(Method.java:566) ~[?:?]
        at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:316) ~[spigot-1.14.4.jar:git-Spigot-56f8471-ccd47a5]
        ... 20 more