Bukkit Plugin Code

Code:
package me.djslin99.mystart;
//imports
import java.io.File;
import java.io.IOException;

import org.bukkit.Bukkit;
import org.bukkit.Location;
import org.bukkit.World;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.configuration.file.FileConfiguration;
import org.bukkit.configuration.file.YamlConfiguration;
import org.bukkit.entity.Player;
import org.bukkit.plugin.java.JavaPlugin;

public class MyStart extends JavaPlugin{

    private File file = new File("plugins/MyStart", "start.yml");
    private FileConfiguration cfg = YamlConfiguration.loadConfiguration(this.file);

    @Override
    public void onEnable() {

    }

    @Override
    public void onDisable() {


    }
    public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args) {
        Player p = (Player) sender;

        //setstart
        if(cmd.getName().equalsIgnoreCase("setstart")) {
            Location loc = p.getLocation();
            String str = "start.";
            this.cfg.set("world", loc.getWorld().getName());
            this.cfg.set(str + "x", loc.getX());
            this.cfg.set(str + "y", loc.getY());
            this.cfg.set(str + "z", loc.getZ());
            this.cfg.set(str + "yaw", loc.getYaw());
            this.cfg.set(str + "pitch", loc.getPitch());
            try {
                this.cfg.save(this.file);
                p.sendMessage("§aStartpunkt gesetzt");
                return true;

                } catch (IOException e) {

                e.printStackTrace();
            }return true;
        }


        //start
        if (cmd.getName().equalsIgnoreCase("start")) {
            String str = "start.";
            if (p != null) {

            World w = Bukkit.getWorld(this.cfg.getString(str + "world"));
            if (w == null) {
                p.sendMessage("§cDer Startpunkt ist in einer nicht vorhandenen Welt, bitte Administrator benachrichtigen.");
                return true;
            }
            double x = this.cfg.getDouble(str + "x");
            double y = this.cfg.getDouble(str + "y");
            double z = this.cfg.getDouble(str + "z");
            double yaw = this.cfg.getDouble(str + "yaw");
            double pitch = this.cfg.getDouble(str + "pitch");
            Location loc = new Location(w, x, y, z, (float) yaw, (float) pitch);
            p.teleport(loc);
            p.sendMessage("§a>>>>>Willkommrn am Start<<<<<");

        } return true;
        } else {
            p.sendMessage("Test");
            return true;
        }

    }



}




plugin.yml


name: MyStart
version: 1.0
author: djslin99
main: me.djslin99.mystart.MyStart
commands:
     setstart:
          description: Setzt den Startpunkt
          usage: /<command>
     start:
          description: Teleportiert dich zum Start
          usage: /<command>


Fehler:

[SEVERE] null
org.bukkit.command.CommandException: Unhandled exception executing command 'start' in plugin MyStart v1.0
    at org.bukkit.command.PluginCommand.execute(PluginCommand.java:46)
    at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:186)
    at org.bukkit.craftbukkit.v1_4_R1.CraftServer.dispatchCommand(CraftServer.java:514)
    at net.minecraft.server.v1_4_R1.PlayerConnection.handleCommand(PlayerConnection.java:980)
    at net.minecraft.server.v1_4_R1.PlayerConnection.chat(PlayerConnection.java:898)
    at net.minecraft.server.v1_4_R1.PlayerConnection.a(PlayerConnection.java:853)
    at net.minecraft.server.v1_4_R1.Packet3Chat.handle(Packet3Chat.java:44)
    at net.minecraft.server.v1_4_R1.NetworkManager.b(NetworkManager.java:290)
    at net.minecraft.server.v1_4_R1.PlayerConnection.d(PlayerConnection.java:113)
    at net.minecraft.server.v1_4_R1.ServerConnection.b(SourceFile:39)
    at net.minecraft.server.v1_4_R1.DedicatedServerConnection.b(SourceFile:30)
    at net.minecraft.server.v1_4_R1.MinecraftServer.r(MinecraftServer.java:598)
    at net.minecraft.server.v1_4_R1.DedicatedServer.r(DedicatedServer.java:224)
    at net.minecraft.server.v1_4_R1.MinecraftServer.q(MinecraftServer.java:494)
    at net.minecraft.server.v1_4_R1.MinecraftServer.run(MinecraftServer.java:427)
    at net.minecraft.server.v1_4_R1.ThreadServerApplication.run(SourceFile:849)
Caused by: java.lang.NullPointerException
    at org.bukkit.craftbukkit.v1_4_R1.CraftServer.getWorld(CraftServer.java:811)
    at org.bukkit.Bukkit.getWorld(Bukkit.java:168)
    at me.djslin99.mystart.MyStart.onCommand(MyStart.java:61)
    at org.bukkit.command.PluginCommand.execute(PluginCommand.java:44)
    ... 15 more