PTweaks

[SEVERE] Error occurred while disabling Ptweaks v4.0 (Is it up to date?)
java.lang.NullPointerException
	at me.plugin.ptweaks.MonsterLimiter.onDisable(MonsterLimiter.java:115)
	at me.plugin.ptweaks.PerformanceTweaks.onDisable(PerformanceTweaks.java:87)
	at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:219)
	at org.bukkit.plugin.java.JavaPluginLoader.disablePlugin(JavaPluginLoader.java:391)
	at org.bukkit.plugin.SimplePluginManager.disablePlugin(SimplePluginManager.java:400)
	at org.bukkit.plugin.SimplePluginManager.disablePlugins(SimplePluginManager.java:393)
	at org.bukkit.craftbukkit.CraftServer.disablePlugins(CraftServer.java:260)
	at net.minecraft.server.MinecraftServer.stop(MinecraftServer.java:328)
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:437)
	at net.minecraft.server.ThreadServerApplication.run(SourceFile:539)
[SEVERE] java.lang.InterruptedException: sleep interrupted
[SEVERE] 	at java.lang.Thread.sleep(Native Method)
[SEVERE] 	at me.plugin.ptweaks.ChunkPersistance.run(ChunkPersistance.java:168)
[SEVERE] 	at java.lang.Thread.run(Unknown Source)