Plugin Help MultiverseCore help

Hi guys every time I'm trying to import a world on the console says this but the world imports fine!
See console:

Code:

[21:53:14 WARN]: java.lang.NullPointerException
[21:53:14 WARN]: at com.onarandombox.MultiverseCore.utils.WorldManager.saveWorldsConfig(WorldManager.java:819)
[21:53:14 WARN]: at com.onarandombox.MultiverseCore.utils.WorldManager.addWorld(WorldManager.java:276)
[21:53:14 WARN]: at com.onarandombox.MultiverseCore.commands.ImportCommand.runCommand(ImportCommand.java:152)
[21:53:14 WARN]: at com.pneumaticraft.commandhandler.multiverse.CommandHandler.checkAndRunCommand(CommandHandler.java:279)
[21:53:14 WARN]: at com.pneumaticraft.commandhandler.multiverse.CommandHandler.processFoundCommands(CommandHandler.java:143)
[21:53:14 WARN]: at com.pneumaticraft.commandhandler.multiverse.CommandHandler.locateAndRunCommand(CommandHandler.java:93)
[21:53:14 WARN]: at com.onarandombox.MultiverseCore.MultiverseCore.onCommand(MultiverseCore.java:919)
[21:53:14 WARN]: at org.bukkit.command.PluginCommand.execute(PluginCommand.java:44)
[21:53:14 WARN]: at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:141)
[21:53:14 WARN]: at org.bukkit.craftbukkit.v1_8_R1.CraftServer.dispatchCommand(CraftServer.java:646)
[21:53:14 WARN]: at org.bukkit.craftbukkit.v1_8_R1.CraftServer.dispatchServerCommand(CraftServer.java:632)
[21:53:14 WARN]: at net.minecraft.server.v1_8_R1.DedicatedServer.aM(DedicatedServer.java:353)
[21:53:14 WARN]: at net.minecraft.server.v1_8_R1.DedicatedServer.z(DedicatedServer.java:317)
[21:53:14 WARN]: at net.minecraft.server.v1_8_R1.MinecraftServer.y(MinecraftServer.java:634)
[21:53:14 WARN]: at net.minecraft.server.v1_8_R1.MinecraftServer.run(MinecraftServer.java:537)
[21:53:14 WARN]: at java.lang.Thread.run(Unknown Source)
[21:53:14 INFO]: An internal error occurred when attempting to perform this command.
[21:53:14 INFO]: Details were printed to the server console and logs, please add that to your bug report.