VaultSlotsError

2012-01-03 04:11:58 [SEVERE] Could not pass event SIGN_CHANGE to VaultSlots
java.lang.NullPointerException
	at me.sirtyler.VaultSlots.SignChange.onSignChange(SignChange.java:20)
	at org.bukkit.plugin.java.JavaPluginLoader$36.execute(JavaPluginLoader.java:514)
	at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62)
	at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:339)
	at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:1069)
	at net.minecraft.server.Packet130UpdateSign.a(SourceFile:41)
	at net.minecraft.server.NetworkManager.b(NetworkManager.java:226)
	at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:93)
	at org.getspout.spout.SpoutNetServerHandler.a(SpoutNetServerHandler.java:586)
	at net.minecraft.server.NetworkListenThread.a(SourceFile:108)
	at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:527)
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:425)
	at net.minecraft.server.ThreadServerApplication.run(SourceFile:457)