Permissions Plus error

Code:

[SEVERE] null
org.bukkit.command.CommandException: Unhandled exception executing command 'promote' in plugin PermissionsPlus v3.0
    at org.bukkit.command.PluginCommand.execute(PluginCommand.java:37)
    at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:128)
    at org.bukkit.craftbukkit.CraftServer.dispatchCommand(CraftServer.java:287)
    at net.minecraft.server.NetServerHandler.handleCommand(NetServerHandler.java:712)
    at net.minecraft.server.NetServerHandler.chat(NetServerHandler.java:678)
    at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:671)
    at net.minecraft.server.Packet3Chat.a(Packet3Chat.java:32)
    at net.minecraft.server.NetworkManager.b(NetworkManager.java:226)
    at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:75)
    at net.minecraft.server.NetworkListenThread.a(SourceFile:105)
    at net.minecraft.server.MinecraftServer.h(MinecraftServer.java:399)
    at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:309)
    at net.minecraft.server.ThreadServerApplication.run(SourceFile:422)
Caused by: java.lang.NullPointerException: key cannot be null
    at org.apache.commons.collections.bidimap.TreeBidiMap.checkNonNullComparable(TreeBidiMap.java:1263)
    at org.apache.commons.collections.bidimap.TreeBidiMap.doGet(TreeBidiMap.java:491)
    at org.apache.commons.collections.bidimap.TreeBidiMap.get(TreeBidiMap.java:178)
    at net.codej.permissionsplus.PermissionsPlus.rankOf(PermissionsPlus.java:1311)
    at net.codej.permissionsplus.PermissionsPlus.onCommand(PermissionsPlus.java:1011)
    at org.bukkit.command.PluginCommand.execute(PluginCommand.java:35)
    ... 12 more

?? any ideas? Im trying to do /promote username

This used to work but know i messed it up.