Code error!?

Hello I have this plugin but it's got an error. here is the error:
Unhandled exception executing command 'pwb MBLobby ke' in pwb: Call to a member function

[PocketMine] [21:16:01] > Unhandled exception executing command 'pwb MBLobby ke' in pwb: Call to a member function getOnlinePlayers() on null
[PocketMine] [21:16:01] > Error: "Call to a member function getOnlinePlayers() on null" (EXCEPTION) in "/phar_PerWorldBroadcast-master_WOZU_qlz9U8gXBR.phar/src/pwb/main" at line 18

Here is the code:

PHP:

<?php
namespace pwb;

use pocketmine\plugin\PluginBase;
use pocketmine\command\Command;
use pocketmine\command\CommandSender;
use pocketmine\Player;
class main extends PluginBase {
    public function onEnable(){
        $this->getLogger()->info("loaded!");
    }
    
    public function onCommand(CommandSender $sender,Command $command, $label,array $args){
        switch ($command->getName()){
            case "pwb":
                if ($sender->hasPermission("pwb.use")){
                if (isset($args[0]) and isset($args[1])){
                    $players = $this->getServer()->getLevelByName($args[0])->getPlayers();
                    unset($args[0]);
                    $message = implode(" ", $args);
                    if (!$players == null){
                        foreach ($players as $player){
                            $player->sendMessage($message);
                        }
                    }else{
                        $sender->sendMessage("no such world");
                    }
                    
                }else{
                    $sender->sendMessage("Usage: /pwb [world] [message]");
                }}else{
                    $sender->sendMessage("No permission to use this command!");
                }
            break;
            
        }
    }
    
}


The line " $players = $this->getServer()->getLevelByName($args[0])->getPlayers(); " is line 18 btw that's where the error is :/ Could someone help?! I have also attached the zip file

Just something completely different I wanna add, wtf happened to the forums? It's a bit messed up in my opinion.

 

There is no -BUTTONS YOU ARE HURTING MY EYES!- getPlayers function in Level. You might want to write your own

PHP:

/* $this must have a getServer function which returns \pocketmine\Server (classes extending pluginBase do */
function aprilFoolsSuck(\fools\pocketmine\level\Level $level): array{
$players = [];
foreach($this->getServer()->getPlayers() as $player){
if($player->getLevel() == $level){
$players[] = $player;
}
return $players;
}
}


Sorry for no formatting and no phpdoc.
April fools btw.