quarantine error1

2012-06-19 13:35:12 [SEVERE] null
org.bukkit.command.CommandException: Unhandled exception executing command 'qjoin' in plugin Quarantine v0.7
	at org.bukkit.command.PluginCommand.execute(PluginCommand.java:42)
	at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:166)
	at org.bukkit.craftbukkit.CraftServer.dispatchCommand(CraftServer.java:479)
	at net.minecraft.server.NetServerHandler.handleCommand(NetServerHandler.java:821)
	at net.minecraft.server.NetServerHandler.chat(NetServerHandler.java:781)
	at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:764)
	at net.minecraft.server.Packet3Chat.handle(Packet3Chat.java:34)
	at net.minecraft.server.NetworkManager.b(NetworkManager.java:229)
	at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:113)
	at net.minecraft.server.NetworkListenThread.a(NetworkListenThread.java:78)
	at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:567)
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:459)
	at net.minecraft.server.ThreadServerApplication.run(SourceFile:492)
Caused by: java.lang.NullPointerException
	at org.bukkit.craftbukkit.CraftWorld.spawnCreature(CraftWorld.java:335)
	at me.DDoS.Quarantine.zone.location.SpawnLocation.spawnCreature(SpawnLocation.java:30)
	at me.DDoS.Quarantine.zone.subzone.SubZone.spawnMob(SubZone.java:81)
	at me.DDoS.Quarantine.zone.subzone.SubZone.spawnStartingMobs(SubZone.java:63)
	at me.DDoS.Quarantine.zone.Zone.spawnStartingMobs(Zone.java:623)
	at me.DDoS.Quarantine.zone.Zone.joinPlayer(Zone.java:510)
	at me.DDoS.Quarantine.command.PlayerCommandExecutor.onCommand(PlayerCommandExecutor.java:66)
	at org.bukkit.command.PluginCommand.execute(PluginCommand.java:40)
	... 12 more