java.lang.NullPointerException
    at net.minecraft.server.WorldNBTStorage.getSeenPlayers(WorldNBTStorage.java:227)
    at net.minecraft.server.ServerConfigurationManagerAbstract.getSeenPlayers(ServerConfigurationManagerAbstract.java:777)
    at net.minecraft.server.MinecraftServer.a(MinecraftServer.java:1036)
    at net.minecraft.server.DedicatedServer.a(DedicatedServer.java:237)
    at net.minecraft.server.MojangStatisticsGenerator.b(SourceFile:91)
    at net.minecraft.server.MinecraftServer.q(MinecraftServer.java:518)
    at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:426)
    at net.minecraft.server.ThreadServerApplication.run(SourceFile:856)