Exception in server tick loop : NullPointerException (Outdated Java)

---- Minecraft Crash Report ----
// Daisy, daisy...

Time: 29.06.13 10:48
Description: Exception in server tick loop

java.lang.NullPointerException
	at alj.f(SourceFile:197)
	at hk.m(SourceFile:665)
	at net.minecraft.server.MinecraftServer.a(SourceFile:873)
	at bko.a(SourceFile:198)
	at ms.b(SourceFile:94)
	at net.minecraft.server.MinecraftServer.s(SourceFile:433)
	at bko.s(SourceFile:124)
	at net.minecraft.server.MinecraftServer.run(SourceFile:339)
	at hf.run(SourceFile:582)