File cannot be null exception

In my plugin i have a command, that should create some things in a config file. I already have a working config file, but i can' t write some things in it from an other class that isn' t the main class. That means for example that someone performs the command "/trampolin create abc". Now im looking, weather this trampolin already exists, and when not, i want to create it. The problem is, that then this error occurs:

Code:

20:37:48 [SCHWERWIEGEND] null
org.bukkit.command.CommandException: Unhandled exception executing command 'tram
polin' in plugin FunnyThings v1.0
        at org.bukkit.command.PluginCommand.execute(PluginCommand.java:42)
        at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:16
6)
        at org.bukkit.craftbukkit.CraftServer.dispatchCommand(CraftServer.java:4
73)
        at net.minecraft.server.NetServerHandler.handleCommand(NetServerHandler.
java:821)
        at net.minecraft.server.NetServerHandler.chat(NetServerHandler.java:781)
 
        at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:764)
        at net.minecraft.server.Packet3Chat.handle(Packet3Chat.java:34)
        at net.minecraft.server.NetworkManager.b(NetworkManager.java:229)
        at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:113)
        at net.minecraft.server.NetworkListenThread.a(NetworkListenThread.java:7
8)
        at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:551)
        at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:449)
        at net.minecraft.server.ThreadServerApplication.run(SourceFile:492)
Caused by: java.lang.IllegalArgumentException: File cannot be null
        at org.bukkit.configuration.file.YamlConfiguration.loadConfiguration(Yam
lConfiguration.java:171)
        at org.bukkit.plugin.java.JavaPlugin.reloadConfig(JavaPlugin.java:117)
        at org.bukkit.plugin.java.JavaPlugin.getConfig(JavaPlugin.java:111)
        at joba97.FunnyThings.commands.trampolin.DeleteTrampolin(trampolin.java:
146)
        at joba97.FunnyThings.commands.trampolin.onCommand(trampolin.java:56)
        at org.bukkit.command.PluginCommand.execute(PluginCommand.java:40)
        ... 12 more

 

Are you using Bukkit's config file handling system?
(http://wiki.bukkit.org/Introduction_to_the_New_Configuration)