[16:13:58] [Server thread/ERROR]: null
org.bukkit.command.CommandException: Unhandled exception executing command 'npcgui' in plugin CitizensGUI v1.1
	at org.bukkit.command.PluginCommand.execute(PluginCommand.java:48) ~[spigot-1.13.2.jar:git-Spigot-e6eb36f-d3ed151]
	at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:141) ~[spigot-1.13.2.jar:git-Spigot-e6eb36f-d3ed151]
	at org.bukkit.craftbukkit.v1_13_R2.CraftServer.dispatchCommand(CraftServer.java:704) ~[spigot-1.13.2.jar:git-Spigot-e6eb36f-d3ed151]
	at net.minecraft.server.v1_13_R2.PlayerConnection.handleCommand(PlayerConnection.java:1620) ~[spigot-1.13.2.jar:git-Spigot-e6eb36f-d3ed151]
	at net.minecraft.server.v1_13_R2.PlayerConnection.a(PlayerConnection.java:1460) ~[spigot-1.13.2.jar:git-Spigot-e6eb36f-d3ed151]
	at net.minecraft.server.v1_13_R2.PacketPlayInChat.a(PacketPlayInChat.java:45) ~[spigot-1.13.2.jar:git-Spigot-e6eb36f-d3ed151]
	at net.minecraft.server.v1_13_R2.PacketPlayInChat.a(PacketPlayInChat.java:1) ~[spigot-1.13.2.jar:git-Spigot-e6eb36f-d3ed151]
	at net.minecraft.server.v1_13_R2.PlayerConnectionUtils.lambda$0(PlayerConnectionUtils.java:9) ~[spigot-1.13.2.jar:git-Spigot-e6eb36f-d3ed151]
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_202]
	at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_202]
	at net.minecraft.server.v1_13_R2.SystemUtils.a(SourceFile:199) [spigot-1.13.2.jar:git-Spigot-e6eb36f-d3ed151]
	at net.minecraft.server.v1_13_R2.MinecraftServer.b(MinecraftServer.java:896) [spigot-1.13.2.jar:git-Spigot-e6eb36f-d3ed151]
	at net.minecraft.server.v1_13_R2.DedicatedServer.b(DedicatedServer.java:417) [spigot-1.13.2.jar:git-Spigot-e6eb36f-d3ed151]
	at net.minecraft.server.v1_13_R2.MinecraftServer.a(MinecraftServer.java:831) [spigot-1.13.2.jar:git-Spigot-e6eb36f-d3ed151]
	at net.minecraft.server.v1_13_R2.MinecraftServer.run(MinecraftServer.java:729) [spigot-1.13.2.jar:git-Spigot-e6eb36f-d3ed151]
	at java.lang.Thread.run(Thread.java:748) [?:1.8.0_202]
Caused by: java.lang.NullPointerException
	at fr.ender_griefeur99.citizensgui.CitizensListGUI.itemMenu(CitizensListGUI.java:145) ~[?:?]
	at fr.ender_griefeur99.citizensgui.CitizensListGUI.setItems(CitizensListGUI.java:85) ~[?:?]
	at fr.ender_griefeur99.citizensgui.CitizensListGUI.<init>(CitizensListGUI.java:73) ~[?:?]
	at fr.ender_griefeur99.citizensgui.Main.onCommand(Main.java:38) ~[?:?]
	at org.bukkit.command.PluginCommand.execute(PluginCommand.java:46) ~[spigot-1.13.2.jar:git-Spigot-e6eb36f-d3ed151]
	... 15 more