Error with trying to create a holographic leaderboard

So basically I'm trying to create a leaderboard that displays the top 10 people who killed the most chickens (lifetime), but it seems like I'm getting an error. Now, I know I horribly messed up somewhere but I don't know where. Also, I'm using the holographic displays API.

Code:

public class PointsManager {

    TutMain f = TutMain.getPlugin(TutMain.class);

    TreeMap<String, Integer> kills = new TreeMap<>();
    FileConfiguration config = f.getConfig();

    public void createLeaderboard(Player player) {
        Hologram holo = HologramsAPI.createHologram(f, player.getLocation());
        holo.insertTextLine(0, ChatColor.YELLOW + "LEADERBOARD OF KILLING CHICKENS");
        for (String s : config.getConfigurationSection("Kills.").getKeys(false)) {
            for (int i = 1; i < 11; i++) {
                Player player1 = Bukkit.getPlayer(s);
                holo.insertTextLine(i, ChatColor.YELLOW + "" + i + ". " + player1.getDisplayName() + ": " + ChatColor.GREEN + "" + kills.values());
            }
        }
    }


}

this is my PointsGetter class if ur interested

Code:

public class PointsGetter implements Listener, CommandExecutor {

    TutMain f = TutMain.getPlugin(TutMain.class);


    @EventHandler
    public void onKill(EntityDeathEvent event) {
        Player player = event.getEntity().getKiller();
        if(event.getEntity() instanceof Chicken) {
            if(event.getEntity().getKiller() == player) {
                if(!f.getConfig().contains("Kills." + player.getName())) {
                    f.getConfig().set("Kills." + player.getName(), 0);
                }
                int kills = f.getConfig().getInt("Kills." + player.getName());

                f.getConfig().set("Kills." + player.getName(), kills+1);
                player.sendMessage(ChatColor.GREEN + "+1 Kill!");
                player.playSound(player.getLocation(), Sound.NOTE_PLING, 1, 1);
            }
        }
    }


    @Override
    public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args) {

        if(!(sender instanceof Player)) return false;

        Player player = (Player) sender;


        if(cmd.getName().equalsIgnoreCase("points")) {
            int kills = f.getConfig().getInt("Kills." + player.getName());
            player.sendMessage(ChatColor.GREEN + "You have " + kills + " Kills!");
            return true;
        }




        return false;
    }
}