Solved Trying to add items to Creative Inventory

I'm trying to add items to the Creative Inventory, but it crashed my server with the error:

Code:

__clone method called on non-object

Full crashdump: https://pastebin.com/e5BUcWTi

My Code
In Main.php, onEnable():

PHP:

BlockFactory::$list[165] = SlimeBlock::class;
ItemBlock::addCreativeItem(new SlimeBlockMCPE());


 

Is it possible to add the Slime Block to the Creative Inventory without creating the block's class? If yes, how? Plus blocks that have a Meta-ID, like 201:2 (Purpur Pillar)?

Spoiler

Slime Blocks (and all other blocks) are already placeable/working, but not added to PocketMine's blocks folder yet.

 

I found it out:

PHP:

ItemBlock::addCreativeItem(Item::get(165));