null
org.bukkit.command.CommandException: Unhandled exception executing command 'ar' in plugin Autorank v3.4
        at org.bukkit.command.PluginCommand.execute(PluginCommand.java:46) ~[spigot.jar:git-Spigot-"606148f"]
        at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:181) ~[spigot.jar:git-Spigot-"606148f"]
        at org.bukkit.craftbukkit.v1_8_R1.CraftServer.dispatchCommand(CraftServer.java:643) ~[spigot.jar:git-Spigot-"606148f"]
        at net.minecraft.server.v1_8_R1.PlayerConnection.handleCommand(PlayerConnection.java:1105) [spigot.jar:git-Spigot-"606148f"]
        at net.minecraft.server.v1_8_R1.PlayerConnection.a(PlayerConnection.java:940) [spigot.jar:git-Spigot-"606148f"]
        at net.minecraft.server.v1_8_R1.PacketPlayInChat.a(PacketPlayInChat.java:26) [spigot.jar:git-Spigot-"606148f"]
        at net.minecraft.server.v1_8_R1.PacketPlayInChat.a(PacketPlayInChat.java:53) [spigot.jar:git-Spigot-"606148f"]
        at net.minecraft.server.v1_8_R1.PacketHandleTask.run(SourceFile:13) [spigot.jar:git-Spigot-"606148f"]
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_31]
        at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_31]
        at net.minecraft.server.v1_8_R1.MinecraftServer.z(MinecraftServer.java:684) [spigot.jar:git-Spigot-"606148f"]
        at net.minecraft.server.v1_8_R1.DedicatedServer.z(DedicatedServer.java:316) [spigot.jar:git-Spigot-"606148f"]
        at net.minecraft.server.v1_8_R1.MinecraftServer.y(MinecraftServer.java:625) [spigot.jar:git-Spigot-"606148f"]
        at net.minecraft.server.v1_8_R1.MinecraftServer.run(MinecraftServer.java:528) [spigot.jar:git-Spigot-"606148f"]
        at java.lang.Thread.run(Thread.java:745) [?:1.8.0_31]
Caused by: java.lang.NullPointerException
        at me.armar.plugins.autorank.requirementhandler.RequirementHandler.getLastKnownGroup(RequirementHandler.java:153) ~[?:?]
        at me.armar.plugins.autorank.commands.CheckCommand.check(CheckCommand.java:52) ~[?:?]
        at me.armar.plugins.autorank.commands.CheckCommand.onCommand(CheckCommand.java:337) ~[?:?]
        at me.armar.plugins.autorank.commands.manager.CommandsManager.onCommand(CommandsManager.java:128) ~[?:?]
        at org.bukkit.command.PluginCommand.execute(PluginCommand.java:44) ~[spigot.jar:git-Spigot-"606148f"]
        ... 14 more