It errors on the line: getServer().createWorld(new WorldCreator("worldname"));

My plugin error:

[10:59:57] [Server thread/INFO]: [Hoi] Enabling Hoi v1.0
[10:59:57] [Server thread/ERROR]: Error occurred while enabling Hoi v1.0 (Is it up to date?)
java.lang.NullPointerException
at net.minecraft.server.v1_8_R2.World.<init>(World.java:197) ~[spigot.jar:git-Spigot-b100cf9-d8a9c7b]
at net.minecraft.server.v1_8_R2.WorldServer.<init>(WorldServer.java:57) ~[spigot.jar:git-Spigot-b100cf9-d8a9c7b]
at org.bukkit.craftbukkit.v1_8_R2.CraftServer.createWorld(CraftServer.java:893) ~[spigot.jar:git-Spigot-b100cf9-d8a9c7b]
at me.myst.Hoi.onEnable(Hoi.java:20) ~[?:?]
at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:321) ~[spigot.jar:git-Spigot-b100cf9-d8a9c7b]
at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:335) [spigot.jar:git-Spigot-b100cf9-d8a9c7b]
at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:405) [spigot.jar:git-Spigot-b100cf9-d8a9c7b]
at org.bukkit.craftbukkit.v1_8_R2.CraftServer.loadPlugin(CraftServer.java:356) [spigot.jar:git-Spigot-b100cf9-d8a9c7b]
at org.bukkit.craftbukkit.v1_8_R2.CraftServer.enablePlugins(CraftServer.java:316) [spigot.jar:git-Spigot-b100cf9-d8a9c7b]
at net.minecraft.server.v1_8_R2.MinecraftServer.r(MinecraftServer.java:420) [spigot.jar:git-Spigot-b100cf9-d8a9c7b]
at net.minecraft.server.v1_8_R2.MinecraftServer.k(MinecraftServer.java:386) [spigot.jar:git-Spigot-b100cf9-d8a9c7b]
at net.minecraft.server.v1_8_R2.MinecraftServer.a(MinecraftServer.java:341) [spigot.jar:git-Spigot-b100cf9-d8a9c7b]
at net.minecraft.server.v1_8_R2.DedicatedServer.init(DedicatedServer.java:257) [spigot.jar:git-Spigot-b100cf9-d8a9c7b]
at net.minecraft.server.v1_8_R2.MinecraftServer.run(MinecraftServer.java:526) [spigot.jar:git-Spigot-b100cf9-d8a9c7b]
at java.lang.Thread.run(Thread.java:745) [?:1.8.0_31]

Multiverse's error:

[11:06:43] [Server thread/WARN]: java.lang.NullPointerException
[11:06:43] [Server thread/WARN]: at net.minecraft.server.v1_8_R2.World.<init>(World.java:197)
[11:06:43] [Server thread/WARN]: at net.minecraft.server.v1_8_R2.WorldServer.<init>(WorldServer.java:57)
[11:06:43] [Server thread/WARN]: at org.bukkit.craftbukkit.v1_8_R2.CraftServer.createWorld(CraftServer.java:893)
[11:06:43] [Server thread/WARN]: at org.bukkit.Bukkit.createWorld(Bukkit.java:463)
[11:06:43] [Server thread/WARN]: at org.bukkit.WorldCreator.createWorld(WorldCreator.java:261)
[11:06:43] [Server thread/WARN]: at com.onarandombox.MultiverseCore.utils.WorldManager.doLoad(WorldManager.java:421)
[11:06:43] [Server thread/WARN]: at com.onarandombox.MultiverseCore.utils.WorldManager.doLoad(WorldManager.java:402)
[11:06:43] [Server thread/WARN]: at com.onarandombox.MultiverseCore.utils.WorldManager.doLoad(WorldManager.java:377)
[11:06:43] [Server thread/WARN]: at com.onarandombox.MultiverseCore.utils.WorldManager.loadWorlds(WorldManager.java:676)
[11:06:43] [Server thread/WARN]: at com.onarandombox.MultiverseCore.MultiverseCore.onEnable(MultiverseCore.java:303)
[11:06:43] [Server thread/WARN]: at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:321)
[11:06:43] [Server thread/WARN]: at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:335)
[11:06:43] [Server thread/WARN]: at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:405)
[11:06:43] [Server thread/WARN]: at org.bukkit.craftbukkit.v1_8_R2.CraftServer.loadPlugin(CraftServer.java:356)
[11:06:43] [Server thread/WARN]: at org.bukkit.craftbukkit.v1_8_R2.CraftServer.enablePlugins(CraftServer.java:316)
[11:06:43] [Server thread/WARN]: at net.minecraft.server.v1_8_R2.MinecraftServer.r(MinecraftServer.java:420)
[11:06:43] [Server thread/WARN]: at net.minecraft.server.v1_8_R2.MinecraftServer.k(MinecraftServer.java:386)
[11:06:43] [Server thread/WARN]: at net.minecraft.server.v1_8_R2.MinecraftServer.a(MinecraftServer.java:341)
[11:06:43] [Server thread/WARN]: at net.minecraft.server.v1_8_R2.DedicatedServer.init(DedicatedServer.java:257)
[11:06:43] [Server thread/WARN]: at net.minecraft.server.v1_8_R2.MinecraftServer.run(MinecraftServer.java:526)
[11:06:43] [Server thread/WARN]: at java.lang.Thread.run(Unknown Source)
[11:06:43] [Server thread/ERROR]: [Multiverse-Core] The world 'S5' could NOT be loaded because it contains errors!
[11:06:43] [Server thread/ERROR]: [Multiverse-Core] Try using Chukster to repair your world! 'S5'
[11:06:43] [Server thread/ERROR]: [Multiverse-Core] http://forums.bukkit.org/threads/admin-chunkster.8186/