[2014-01-23 11:17:40] [Server thread/INFO] An unknown error occurred while attempting to perform this command
[2014-01-23 11:17:40] [Server thread/ERROR] Couldn't process command
java.lang.NullPointerException
        at bu.a(SourceFile:86) ~[minecraft_server.jar:?]
        at v.a(SourceFile:435) ~[minecraft_server.jar:?]
        at v.a(SourceFile:430) ~[minecraft_server.jar:?]
        at cc.b(SourceFile:19) ~[minecraft_server.jar:?]
        at x.a(SourceFile:65) [minecraft_server.jar:?]
        at md.aw(SourceFile:297) [minecraft_server.jar:?]
        at md.a(SourceFile:224) [minecraft_server.jar:?]
        at net.minecraft.server.MinecraftServer.run(SourceFile:385) [minecraft_server.jar:?]
        at lt.run(SourceFile:647) [minecraft_server.jar:?]

[2014-01-23 11:18:11] [Server Shutdown Thread/INFO] Stopping server
[2014-01-23 11:18:11] [Server Shutdown Thread/INFO] Saving worlds
Exception in thread "Server Shutdown Thread" java.lang.NullPointerException
        at net.minecraft.server.MinecraftServer.a(SourceFile:289)
        at net.minecraft.server.MinecraftServer.n(SourceFile:317)
        at ls.run(SourceFile:635)