scheduleAsyncRepeatingTask won't work anymore and drops warnings in console

Hi Plugin Coders,
I have a problem regarding the function Bukkit.getServer().scheduleAsyncRepeatingTask. It checks every 2 seconds if any player wears a specific helmet and if so, the player is granted a regeneration effect.

Code:

Bukkit.getScheduler().scheduleAsyncRepeatingTask(this, new BukkitRunnable() {
            public void run() {
                for (Player current : Bukkit.getOnlinePlayers()) {
                    if (current.getInventory().getHelmet().getItemMeta().getDisplayName().equals("§6Crown")) {
                        current.addPotionEffect(new PotionEffect(PotionEffectType.REGENERATION, tics, 1));
                    }
                }
            }
        }, 0, tics);

The function as it is used to be working, but after changing the code and then ctrl+z-ing back this shit just stopped working and I am starting to lose my mind. Sorry for inappropriate language. Please help, I also added SuppressWarnings for deprecation
The console warning:
[22:16:01 WARN]: Exception in thread "pool-3-thread-297"
[22:16:01 WARN]: org.apache.commons.lang.UnhandledException: Plugin minecraft_plugin1 v1.0 generated an exception while executing task 2
at org.bukkit.craftbukkit.v1_8_R3.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:56)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.NullPointerException
at de.manu.minecraft_plugin1.main.Main$1.run(Main.java:47)
at org.bukkit.craftbukkit.v1_8_R3.scheduler.CraftTask.run(CraftTask.java:53)
at org.bukkit.craftbukkit.v1_8_R3.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:53)
... 3 more

and it occurs every 2 seconds.

 

Thanks for your reply.
It is intended to do nothing if the player doesn't wear the Helmet named "§6Crown", it's a ShapedRecipe that you can craft. If a player is wearing it, the player should be granted a potion. Doing it sync instead of async won't solve the problem either, I already tried that.

 

I did not change the code in any way and as I started it up today, it worked fine for some reason... Thank you for your help tho.