pocketmine\level\weather\WeatherManager::isRegistered PHP Method

    public static function isRegistered(Level $level)
    {
        if (isset(self::$registeredLevel[$level->getName()])) {
            return true;
        }
        return false;
    }

 public function execute(CommandSender $sender, $currentAlias, array $args)
 {
     if (!$this->testPermission($sender)) {
         return true;
     }
     if (count($args) < 1) {
         $sender->sendMessage(new TranslationContainer("commands.generic.usage", [$this->usageMessage]));
         return false;
     }
     if ($sender instanceof Player) {
         $wea = (int) $args[0];
         if ($wea >= 0 and $wea <= 3) {
             if (WeatherManager::isRegistered($sender->getLevel())) {
                 $sender->getLevel()->getWeather()->setWeather($wea);
                 $sender->sendMessage(TextFormat::GREEN . "Weather changed successfully for " . $sender->getLevel()->getFolderName());
                 return true;
             } else {
                 $sender->sendMessage(TextFormat::RED . $sender->getLevel()->getFolderName() . " hasn't registered to WeatherManager.");
                 return false;
             }
         } else {
             $sender->sendMessage(TextFormat::RED . "Invalid weather.");
             return false;
         }
     }
     if (count($args) < 2) {
         $sender->sendMessage(TextFormat::RED . "Wrong parameters.");
         return false;
     }
     $level = $sender->getServer()->getLevelByName($args[0]);
     if (!$level instanceof Level) {
         $sender->sendMessage(TextFormat::RED . "Invalid level name.");
         return false;
     }
     $wea = (int) $args[1];
     if ($wea >= 0 and $wea <= 3) {
         if (WeatherManager::isRegistered($level)) {
             $level->getWeather()->setWeather($wea);
             $sender->sendMessage(TextFormat::GREEN . "Weather changed successfully for " . $level->getFolderName());
             return true;
         } else {
             $sender->sendMessage(TextFormat::RED . $level->getFolderName() . " hasn't registered to WeatherManager.");
             return false;
         }
     } else {
         $sender->sendMessage(TextFormat::RED . "Invalid weather.");
         return false;
     }
     return true;
 }