23:43:38 [SEVERE] null
org.bukkit.command.CommandException: Unhandled exception executing command 'whisper' in plugin CommandBook v1.6-customized
        at org.bukkit.command.PluginCommand.execute(PluginCommand.java:42)
        at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:163)
        at org.bukkit.craftbukkit.CraftServer.dispatchCommand(CraftServer.java:358)
        at net.minecraft.server.NetServerHandler.handleCommand(NetServerHandler.java:757)
        at net.minecraft.server.NetServerHandler.chat(NetServerHandler.java:722)
        at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:715)
        at net.minecraft.server.Packet3Chat.a(Packet3Chat.java:33)
        at net.minecraft.server.NetworkManager.b(NetworkManager.java:226)
        at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:92)
        at org.getspout.spout.SpoutNetServerHandler.a(SpoutNetServerHandler.java:500)
        at net.minecraft.server.NetworkListenThread.a(SourceFile:108)
        at net.minecraft.server.MinecraftServer.h(MinecraftServer.java:471)
        at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:374)
        at net.minecraft.server.ThreadServerApplication.run(SourceFile:417)
Caused by: java.lang.NullPointerException
        at com.sk89q.commandbook.CommandBookPlugin.onCommand(CommandBookPlugin.java:266)
        at org.bukkit.command.PluginCommand.execute(PluginCommand.java:40)
        ... 13 more