Load only chunks around spawn

I want to load chunks only 40 blocks around of my spawn because when pmmp load more chunks I get structures like this in my void world:

Spoiler

ChunkLoadEvent is not cancellable and also it has only isNewChunk function, so how I do it then?
I don't have any tries to do it at all..

 

I've tried this, but don't work

PHP:

public function onChunkLoad(\pocketmine\event\level\ChunkLoadEvent $e){
        $chunk = $e->getChunk();
        if($e->getChunk()->getZ() > 150){
            echo 'UNLOADING CHUNK';
            $chunk->unload(false, false);
        }
       
  }


 

You must be using a custom world generator?

 

Unloading chunks from inside the chunk does not unload them from the level, just like unloading a level from inside the level does not unload the level from the server.

To fix this, try instead to unload the chunk from the level:
https://github.com/PocketMine/PocketMine-MP/blob/master/src/pocketmine/level/Level.php#L2545