NPE thrown even with null checks in bukkit/spigiot plugin

Question

I am getting an error on my spigiot(based on bukkit) plugin that I was developing. I followed a code tutorial on a minigame plugin and downloaded the source code()which worked fine. I edited the code after and added my own weapon and started developing a multi-player spawn system. Now, when I left the game, I get a null pointer exception, even with the checks I put in place after getting this the first time.

[11:36:49] [Server thread/INFO]: Zippynik issued server command: /mb l 1[11:36:49] [Server thread/ERROR]: nullorg.bukkit.command.CommandException: Unhandled exception executing command 'mb' in plugin MagicBattle v1.2.0at org.bukkit.command.PluginCommand.execute(PluginCommand.java:46) ~[craftbukkit-1.8.8-R0.1.jar:git-Bukkit-d3e0b6f]at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:140) ~[craftbukkit-1.8.8-R0.1.jar:git-Bukkit-d3e0b6f]at org.bukkit.craftbukkit.v1_8_R3.CraftServer.dispatchCommand(CraftServer.java:620) ~[craftbukkit-1.8.8-R0.1.jar:git-Bukkit-d3e0b6f]at net.minecraft.server.v1_8_R3.PlayerConnection.handleCommand(PlayerConnection.java:1106) [craftbukkit-1.8.8-R0.1.jar:git-Bukkit-d3e0b6f]at net.minecraft.server.v1_8_R3.PlayerConnection.a(PlayerConnection.java:966) [craftbukkit-1.8.8-R0.1.jar:git-Bukkit-d3e0b6f]at net.minecraft.server.v1_8_R3.PacketPlayInChat.a(SourceFile:37) [craftbukkit-1.8.8-R0.1.jar:git-Bukkit-d3e0b6f]at net.minecraft.server.v1_8_R3.PacketPlayInChat.a(SourceFile:9) [craftbukkit-1.8.8-R0.1.jar:git-Bukkit-d3e0b6f]at net.minecraft.server.v1_8_R3.PlayerConnectionUtils$1.run(SourceFile:13) [craftbukkit-1.8.8-R0.1.jar:git-Bukkit-d3e0b6f]at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) [?:1.7.0_80]at java.util.concurrent.FutureTask.run(Unknown Source) [?:1.7.0_80]at net.minecraft.server.v1_8_R3.SystemUtils.a(SourceFile:44) [craftbukkit-1.8.8-R0.1.jar:git-Bukkit-d3e0b6f]at net.minecraft.server.v1_8_R3.MinecraftServer.B(MinecraftServer.java:673) [craftbukkit-1.8.8-R0.1.jar:git-Bukkit-d3e0b6f]at net.minecraft.server.v1_8_R3.DedicatedServer.B(DedicatedServer.java:335) [craftbukkit-1.8.8-R0.1.jar:git-Bukkit-d3e0b6f]at net.minecraft.server.v1_8_R3.MinecraftServer.A(MinecraftServer.java:629) [craftbukkit-1.8.8-R0.1.jar:git-Bukkit-d3e0b6f]at net.minecraft.server.v1_8_R3.MinecraftServer.run(MinecraftServer.java:537) [craftbukkit-1.8.8-R0.1.jar:git-Bukkit-d3e0b6f]at java.lang.Thread.run(Unknown Source) [?:1.7.0_80]Caused by: java.lang.NullPointerExceptionat me.pogostick29dev.magicbattle.PlayerData.restorePlayer(Arena.java:212) ~[?:?]at me.pogostick29dev.magicbattle.Arena.removePlayer(Arena.java:86) ~[?:?]at me.pogostick29dev.magicbattle.commands.Leave.onCommand(Leave.java:17) ~[?:?]at me.pogostick29dev.magicbattle.CommandManager.onCommand(CommandManager.java:65) ~[?:?]at org.bukkit.command.PluginCommand.execute(PluginCommand.java:44) ~[craftbukkit-1.8.8-R0.1.jar:git-Bukkit-d3e0b6f]... 15 more

Heres the code for the PlayerData class(part of Arena.java)

    public int playerNumber;
    private Player puu;
    private String playerName;
    private ItemStack[] contents, armorContents;
    private Location location;

    protected PlayerData(Player p,int pnum) {
        this.playerName = p.getName();
        this.contents = p.getInventory().getContents();
        this.armorContents = p.getInventory().getArmorContents();
        this.location = p.getLocation();
        this.playerNumber = pnum;
        this.puu = p;
    }

    protected Player getPlayer() {
        return puu;
    }

    protected void restorePlayer() {
        Player p;
        if (puu != null){
         p = puu;}
        else{

            Bukkit.broadcastMessage("puu is invalid");
            return;
        }
        if (contents !=null){
        p.getInventory().setContents(contents);}
        if (armorContents !=null){
        p.getInventory().setArmorContents(armorContents);}
        if (location !=null){
        p.teleport(location);}
        return;
        }


    protected boolean isForPlayer(Player p) {
        return playerName.equalsIgnoreCase(p.getName());
    }


}

, for the Arena class code concerning leaving the arena.

public void removePlayer(Player p) {
        if(getPlayerData(p) !=null){
        PlayerData d = getPlayerData(p);
        d.restorePlayer();
        data.remove(d);
        }else{
            Bukkit.broadcastMessage("PlayerData is null");
        }
        currentPlayers--;

        for (Sign s : signs) {
            s.setLine(2, currentPlayers + "");
            s.update();
        }

        if (currentPlayers == 1) {
            stop(data.get(0).getPlayer());
        } else if (currentPlayers == 0) {
            stop();
        }
    }

and finally for Leave.java

        public class Leave extends MagicCommand {

        public void onCommand(Player p, String[] args) {
            if (ArenaManager.getInstance().getArena(p) == null) {
                MessageManager.getInstance().msg(p, MessageType.BAD, "You are not already in an arena!");
                return;
            }

            ArenaManager.getInstance().getArena(p).removePlayer(p);
        }
        public Leave() {
            super("Leave an arena.", "", "l");
        }
    }

if you need anything else, its on github https://github.com/Zippynik/MagicBattle

Edit: 212 the beggining of restorePlayer 86 the beggining of RemovePlayer 17: Beginning of ArenaManager.getInstance().getArena(p).removePlayer(p);

Edit 2: Added null checks for all variables used in restorePlayer and removePlayer... Still returning null. Could the problem be ArenaManager.getInstance() or getArena()