Error when registering command

So im starting on a plugin but im getting an error, Here the error & code:

Error:

Code:

2013-01-20 19:24:54 [INFO] Starting minecraft server version 1.4.6
2013-01-20 19:24:54 [INFO] Loading properties
2013-01-20 19:24:54 [INFO] Default game type: SURVIVAL
2013-01-20 19:24:54 [INFO] Generating keypair
2013-01-20 19:24:55 [INFO] Starting Minecraft server on *:25565
2013-01-20 19:24:55 [INFO] This server is running CraftBukkit version git-Bukkit-1.4.6-R0.1-b2561jnks (MC: 1.4.6) (Implementing API version 1.4.6-R0.1)
2013-01-20 19:24:55 [INFO] [ReserveMe] Loading ReserveMe v1.0
2013-01-20 19:24:55 [INFO] [AdvanceKick] Loading AdvanceKick v1.0
2013-01-20 19:24:55 [INFO] Preparing level "world"
2013-01-20 19:24:55 [INFO] ----- Bukkit Auto Updater -----
2013-01-20 19:24:55 [INFO] It appears that you're running a Beta Build, when you've specified in bukkit.yml that you prefer to run Recommended Builds.
2013-01-20 19:24:55 [INFO] If you would like to be kept informed about new Beta Build releases, it is recommended that you change 'preferred-channel' in your bukkit.yml to 'beta'.
2013-01-20 19:24:55 [INFO] With that set, you will be told whenever a new version is available for download, so that you can always keep up to date and secure with the latest fixes.
2013-01-20 19:24:55 [INFO] If you would like to disable this warning, simply set 'suggest-channels' to false in bukkit.yml.
2013-01-20 19:24:55 [INFO] ----- ------------------- -----
2013-01-20 19:24:55 [INFO] Preparing start region for level 0 (Seed: -8375517133147294036)
2013-01-20 19:24:56 [INFO] Preparing spawn area: 40%
2013-01-20 19:24:57 [INFO] [ReserveMe] Enabling ReserveMe v1.0
2013-01-20 19:24:57 [INFO] [ReserveMe] Plugin successfully enabled.
2013-01-20 19:24:57 [SEVERE] Error occurred while enabling ReserveMe v1.0 (Is it up to date?)
java.lang.NullPointerException
    at me.thedbcoders.reserveme.main.onEnable(main.java:21)
    at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:217)
    at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:457)
    at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:381)
    at org.bukkit.craftbukkit.v1_4_6.CraftServer.loadPlugin(CraftServer.java:278)
    at org.bukkit.craftbukkit.v1_4_6.CraftServer.enablePlugins(CraftServer.java:260)
    at net.minecraft.server.v1_4_6.MinecraftServer.j(MinecraftServer.java:321)
    at net.minecraft.server.v1_4_6.MinecraftServer.e(MinecraftServer.java:300)
    at net.minecraft.server.v1_4_6.MinecraftServer.a(MinecraftServer.java:259)
    at net.minecraft.server.v1_4_6.DedicatedServer.init(DedicatedServer.java:149)
    at net.minecraft.server.v1_4_6.MinecraftServer.run(MinecraftServer.java:399)
    at net.minecraft.server.v1_4_6.ThreadServerApplication.run(SourceFile:849)
2013-01-20 19:24:57 [INFO] [AdvanceKick] Enabling AdvanceKick v1.0
2013-01-20 19:24:57 [INFO] [AdvanceKick] Plugin loaded.
2013-01-20 19:24:57 [INFO] Server permissions file permissions.yml is empty, ignoring it
2013-01-20 19:24:57 [INFO] Done (1.835s)! For help, type "help" or "?"

Main class:

Code:

package me.thedbcoders.reserveme;
 
import java.util.HashSet;
import java.util.logging.Logger;
 
import me.thedbcoders.reserveme.commands.reserveme;
import me.thedbcoders.reserveme.events.join;
 
import org.bukkit.Bukkit;
import org.bukkit.plugin.PluginManager;
import org.bukkit.plugin.java.JavaPlugin;
 
public class main extends JavaPlugin{
public String prefix = "[ReserveMe] ";
public PluginManager pm = Bukkit.getServer().getPluginManager();
public static final Logger mclog = Logger.getLogger("Minecraft");
public HashSet <String> reservedplayers = new HashSet <String >();
public int reserved = 0;
public void onEnable(){
mclog.info(prefix + "Plugin successfully enabled.");
this.getCommand("reserveme").setExecutor(new reserveme(this));
registerEvents();
}
public void onDisable(){
mclog.info(prefix + "Plugin successfully disabled.");
this.reserved = 0;
this.reservedplayers.clear();
}
public void registerEvents(){
//
//new join(this);
}
}

Command class:

Code:

package me.thedbcoders.reserveme.commands;
 
import org.bukkit.ChatColor;
import org.bukkit.command.Command;
import org.bukkit.command.CommandExecutor;
import org.bukkit.command.CommandSender;
import org.bukkit.entity.Player;
 
import me.thedbcoders.reserveme.main;
 
public class reserveme implements CommandExecutor {
public static main plugin;
public reserveme(main instance){
plugin = instance;
}
public boolean onCommand(CommandSender sender, Command cmd, String CommandLabel, String[] args){
if(cmd.getName().equalsIgnoreCase("reserveme")){
if(sender instanceof Player){
if(args.length == 0){
if(plugin.reservedplayers.contains(sender.getName())){
sender.sendMessage(ChatColor.GREEN + "You are already reserved!");
}else{
plugin.reservedplayers.add(sender.getName());
plugin.reserved++;
sender.sendMessage(ChatColor.GREEN + "You are now reserved!");
}
}else{
sender.sendMessage(ChatColor.RED + "Wrong usage, /reserveme");
}
}
if(!(sender instanceof Player)){
sender.sendMessage("This is an ingame command, Console commands comming soon!");
}
}
return false;
}
}

 

ThedbCoders It appears that you've forgotten to add the command to your plugin.yml.
http://wiki.bukkit.org/Plugin_Tutorial#Adding_your_Command_to_the_Plugin.yml