Prism [SEVERE] null

2013-03-22 19:39:25 [INFO] tubelius issued server command: /pr preview cancel
2013-03-22 19:39:25 [SEVERE] null
org.bukkit.command.CommandException: Unhandled exception executing command 'pr' in plugin Prism v1.5.5
at org.bukkit.command.PluginCommand.execute(PluginCommand.java:46)
at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:187)
at org.bukkit.craftbukkit.v1_5_R2.CraftServer.dispatchCommand(CraftServer.java:523)
at net.minecraft.server.v1_5_R2.PlayerConnection.handleCommand(PlayerConnection.java:967)
at net.minecraft.server.v1_5_R2.PlayerConnection.chat(PlayerConnection.java:885)
at net.minecraft.server.v1_5_R2.PlayerConnection.a(PlayerConnection.java:840)
at net.minecraft.server.v1_5_R2.Packet3Chat.handle(Packet3Chat.java:44)
at net.minecraft.server.v1_5_R2.NetworkManager.b(NetworkManager.java:292)
at net.minecraft.server.v1_5_R2.PlayerConnection.d(PlayerConnection.java:113)
at net.minecraft.server.v1_5_R2.ServerConnection.b(SourceFile:35)
at net.minecraft.server.v1_5_R2.DedicatedServerConnection.b(SourceFile:30)
at net.minecraft.server.v1_5_R2.MinecraftServer.r(MinecraftServer.java:580)
at net.minecraft.server.v1_5_R2.DedicatedServer.r(DedicatedServer.java:225)
at net.minecraft.server.v1_5_R2.MinecraftServer.q(MinecraftServer.java:476)
at net.minecraft.server.v1_5_R2.MinecraftServer.run(MinecraftServer.java:409)
at net.minecraft.server.v1_5_R2.ThreadServerApplication.run(SourceFile:573)
Caused by: java.lang.NullPointerException
at me.botsko.prism.appliers.Preview.cancel_preview(Preview.java:145)
at me.botsko.prism.commands.PreviewCommand.handle(PreviewCommand.java:65)
at me.botsko.prism.commandlibs.Executor.onCommand(Executor.java:107)
at org.bukkit.command.PluginCommand.execute(PluginCommand.java:44)
... 15 more

2013-03-22 19:40:46 [INFO] Prism version 1.5.5
2013-03-22 19:40:47 [INFO] This server is running CraftBukkit version git-Bukkit-1.4.7-R1.0-59-ge869277-b2700jnks (MC: 1.5.1) (Implementing API version 1.5.1-R0.1-SNAPSHOT)