How to check if armor inventory slot is not empty

As title suggests, i wanna know of armor inv slot is not empty.
I tried this code
if($sender->getArmorInventory()->getHelmet() !== null)
But no luck

 

PHP:

use pocketmine\item\Helmet;

if($sender->getArmorInventory()->getHelmet() instanceof Helmet){
}


 

There is no such class...

A simple way is to do

PHP:

if(!$sender->getArmorInventory()->getHelmet()->isNull())

 

If I was you, I would

PHP:

if(!is_null($player->getArmorInventory()->getHelmet())){
}

 

Now i got another problem. How can i transfer armor inventory item to player inventory if that item already exist in armor inventory.
I hope anyone won't hard time understanding this lol

 

Ex. A player has helmet with custom name in inventory. If i do getArmorInventory->setHelmet it will override that item in inventory.What i want to do is transfer it to player inventory.

 

Simple

PHP:

$player->getInventory()->addItem($player->getArmorInventory()->getHelmet());
//set helmet