diff --git a/src/pocketmine/Player.php b/src/pocketmine/Player.php
index 4432a58a2d..7906844819 100644
--- a/src/pocketmine/Player.php
+++ b/src/pocketmine/Player.php
@@ -609,7 +609,7 @@ class Player extends Human implements CommandSender, ChunkLoader, ChunkListener,
 	 *
 	 * @return PermissionAttachment
 	 */
-	public function addAttachment(Plugin $plugin, string $name = null, bool $value = null) : PermissionAttachment{
+	public function addAttachment(Plugin $plugin, ?string $name = null, ?bool $value = null) : PermissionAttachment{
 		return $this->perm->addAttachment($plugin, $name, $value);
 	}
 
@@ -910,7 +910,7 @@ class Player extends Human implements CommandSender, ChunkLoader, ChunkListener,
 		return false;
 	}
 
-	protected function unloadChunk(int $x, int $z, Level $level = null){
+	protected function unloadChunk(int $x, int $z, ?Level $level = null){
 		$level = $level ?? $this->level;
 		$index = Level::chunkHash($x, $z);
 		if(isset($this->usedChunks[$index])){
@@ -3132,7 +3132,7 @@ class Player extends Human implements CommandSender, ChunkLoader, ChunkListener,
 		return $result;
 	}
 
-	public function sendPosition(Vector3 $pos, float $yaw = null, float $pitch = null, int $mode = MovePlayerPacket::MODE_NORMAL, array $targets = null){
+	public function sendPosition(Vector3 $pos, ?float $yaw = null, ?float $pitch = null, int $mode = MovePlayerPacket::MODE_NORMAL, ?array $targets = null){
 		$yaw = $yaw ?? $this->yaw;
 		$pitch = $pitch ?? $this->pitch;
 
@@ -3156,7 +3156,7 @@ class Player extends Human implements CommandSender, ChunkLoader, ChunkListener,
 	/**
 	 * {@inheritdoc}
 	 */
-	public function teleport(Vector3 $pos, float $yaw = null, float $pitch = null) : bool{
+	public function teleport(Vector3 $pos, ?float $yaw = null, ?float $pitch = null) : bool{
 		if(parent::teleport($pos, $yaw, $pitch)){
 
 			$this->removeAllWindows();
@@ -3298,7 +3298,7 @@ class Player extends Human implements CommandSender, ChunkLoader, ChunkListener,
 	 * @throws \InvalidArgumentException if a forceID which is already in use is specified
 	 * @throws \InvalidStateException if trying to add a window without forceID when no slots are free
 	 */
-	public function addWindow(Inventory $inventory, int $forceId = null, bool $isPermanent = false) : int{
+	public function addWindow(Inventory $inventory, ?int $forceId = null, bool $isPermanent = false) : int{
 		if(($id = $this->getWindowId($inventory)) !== ContainerIds::NONE){
 			return $id;
 		}
diff --git a/src/pocketmine/Server.php b/src/pocketmine/Server.php
index 12bf3f5225..10d8302fc4 100644
--- a/src/pocketmine/Server.php
+++ b/src/pocketmine/Server.php
@@ -1333,7 +1333,7 @@ class Server{
 	 *
 	 * @return int
 	 */
-	public function broadcastMessage($message, array $recipients = null) : int{
+	public function broadcastMessage($message, ?array $recipients = null) : int{
 		if(!is_array($recipients)){
 			return $this->broadcast($message, self::BROADCAST_CHANNEL_USERS);
 		}
@@ -1363,7 +1363,7 @@ class Server{
 	 *
 	 * @return int
 	 */
-	public function broadcastTip(string $tip, array $recipients = null) : int{
+	public function broadcastTip(string $tip, ?array $recipients = null) : int{
 		$recipients = $recipients ?? $this->selectPermittedPlayers(self::BROADCAST_CHANNEL_USERS);
 
 		/** @var Player[] $recipients */
@@ -1380,7 +1380,7 @@ class Server{
 	 *
 	 * @return int
 	 */
-	public function broadcastPopup(string $popup, array $recipients = null) : int{
+	public function broadcastPopup(string $popup, ?array $recipients = null) : int{
 		$recipients = $recipients ?? $this->selectPermittedPlayers(self::BROADCAST_CHANNEL_USERS);
 
 		/** @var Player[] $recipients */
@@ -1401,7 +1401,7 @@ class Server{
 	 *
 	 * @return int
 	 */
-	public function broadcastTitle(string $title, string $subtitle = "", int $fadeIn = -1, int $stay = -1, int $fadeOut = -1, array $recipients = null) : int{
+	public function broadcastTitle(string $title, string $subtitle = "", int $fadeIn = -1, int $stay = -1, int $fadeOut = -1, ?array $recipients = null) : int{
 		$recipients = $recipients ?? $this->selectPermittedPlayers(self::BROADCAST_CHANNEL_USERS);
 
 		/** @var Player[] $recipients */
@@ -1916,7 +1916,7 @@ class Server{
 	 * @param string        $xboxUserId
 	 * @param Player[]|null $players
 	 */
-	public function updatePlayerListData(UUID $uuid, int $entityId, string $name, Skin $skin, string $xboxUserId = "", array $players = null){
+	public function updatePlayerListData(UUID $uuid, int $entityId, string $name, Skin $skin, string $xboxUserId = "", ?array $players = null){
 		$pk = new PlayerListPacket();
 		$pk->type = PlayerListPacket::TYPE_ADD;
 
@@ -1929,7 +1929,7 @@ class Server{
 	 * @param UUID          $uuid
 	 * @param Player[]|null $players
 	 */
-	public function removePlayerListData(UUID $uuid, array $players = null){
+	public function removePlayerListData(UUID $uuid, ?array $players = null){
 		$pk = new PlayerListPacket();
 		$pk->type = PlayerListPacket::TYPE_REMOVE;
 		$pk->entries[] = PlayerListEntry::createRemovalEntry($uuid);
diff --git a/src/pocketmine/Thread.php b/src/pocketmine/Thread.php
index 347ec62bcd..a51ba123f9 100644
--- a/src/pocketmine/Thread.php
+++ b/src/pocketmine/Thread.php
@@ -39,7 +39,7 @@ abstract class Thread extends \Thread{
 		return $this->classLoader;
 	}
 
-	public function setClassLoader(\ClassLoader $loader = null){
+	public function setClassLoader(?\ClassLoader $loader = null){
 		$this->composerAutoloaderPath = \pocketmine\COMPOSER_AUTOLOADER_PATH;
 
 		if($loader === null){
diff --git a/src/pocketmine/Worker.php b/src/pocketmine/Worker.php
index f4018ea48f..ee62a05400 100644
--- a/src/pocketmine/Worker.php
+++ b/src/pocketmine/Worker.php
@@ -39,7 +39,7 @@ abstract class Worker extends \Worker{
 		return $this->classLoader;
 	}
 
-	public function setClassLoader(\ClassLoader $loader = null){
+	public function setClassLoader(?\ClassLoader $loader = null){
 		$this->composerAutoloaderPath = \pocketmine\COMPOSER_AUTOLOADER_PATH;
 
 		if($loader === null){
diff --git a/src/pocketmine/command/Command.php b/src/pocketmine/command/Command.php
index 0cea12cd9b..02ab7989ae 100644
--- a/src/pocketmine/command/Command.php
+++ b/src/pocketmine/command/Command.php
@@ -79,7 +79,7 @@ abstract class Command{
 	 * @param string   $usageMessage
 	 * @param string[] $aliases
 	 */
-	public function __construct(string $name, string $description = "", string $usageMessage = null, array $aliases = []){
+	public function __construct(string $name, string $description = "", ?string $usageMessage = null, array $aliases = []){
 		$this->name = $name;
 		$this->setLabel($name);
 		$this->setDescription($description);
diff --git a/src/pocketmine/command/CommandMap.php b/src/pocketmine/command/CommandMap.php
index 837d6e2bdb..9583b4e83a 100644
--- a/src/pocketmine/command/CommandMap.php
+++ b/src/pocketmine/command/CommandMap.php
@@ -39,7 +39,7 @@ interface CommandMap{
 	 *
 	 * @return bool
 	 */
-	public function register(string $fallbackPrefix, Command $command, string $label = null) : bool;
+	public function register(string $fallbackPrefix, Command $command, ?string $label = null) : bool;
 
 	/**
 	 * @param CommandSender $sender
diff --git a/src/pocketmine/command/ConsoleCommandSender.php b/src/pocketmine/command/ConsoleCommandSender.php
index 119c55fef2..8db5aa74db 100644
--- a/src/pocketmine/command/ConsoleCommandSender.php
+++ b/src/pocketmine/command/ConsoleCommandSender.php
@@ -71,7 +71,7 @@ class ConsoleCommandSender implements CommandSender{
 	 *
 	 * @return PermissionAttachment
 	 */
-	public function addAttachment(Plugin $plugin, string $name = null, bool $value = null) : PermissionAttachment{
+	public function addAttachment(Plugin $plugin, ?string $name = null, ?bool $value = null) : PermissionAttachment{
 		return $this->perm->addAttachment($plugin, $name, $value);
 	}
 
diff --git a/src/pocketmine/command/SimpleCommandMap.php b/src/pocketmine/command/SimpleCommandMap.php
index d7296f82f8..523089d658 100644
--- a/src/pocketmine/command/SimpleCommandMap.php
+++ b/src/pocketmine/command/SimpleCommandMap.php
@@ -151,7 +151,7 @@ class SimpleCommandMap implements CommandMap{
 	 *
 	 * @return bool
 	 */
-	public function register(string $fallbackPrefix, Command $command, string $label = null) : bool{
+	public function register(string $fallbackPrefix, Command $command, ?string $label = null) : bool{
 		if($label === null){
 			$label = $command->getName();
 		}
diff --git a/src/pocketmine/command/defaults/ParticleCommand.php b/src/pocketmine/command/defaults/ParticleCommand.php
index 12b939eb39..c9ea96da11 100644
--- a/src/pocketmine/command/defaults/ParticleCommand.php
+++ b/src/pocketmine/command/defaults/ParticleCommand.php
@@ -141,7 +141,7 @@ class ParticleCommand extends VanillaCommand{
 	 *
 	 * @return Particle|null
 	 */
-	private function getParticle(string $name, int $data = null){
+	private function getParticle(string $name, ?int $data = null){
 		switch($name){
 			case "explode":
 				return new ExplodeParticle();
diff --git a/src/pocketmine/event/entity/EntityEffectAddEvent.php b/src/pocketmine/event/entity/EntityEffectAddEvent.php
index a42747f75f..d8f5633576 100644
--- a/src/pocketmine/event/entity/EntityEffectAddEvent.php
+++ b/src/pocketmine/event/entity/EntityEffectAddEvent.php
@@ -38,7 +38,7 @@ class EntityEffectAddEvent extends EntityEffectEvent{
 	 * @param EffectInstance $effect
 	 * @param EffectInstance $oldEffect
 	 */
-	public function __construct(Entity $entity, EffectInstance $effect, EffectInstance $oldEffect = null){
+	public function __construct(Entity $entity, EffectInstance $effect, ?EffectInstance $oldEffect = null){
 		parent::__construct($entity, $effect);
 		$this->oldEffect = $oldEffect;
 	}
diff --git a/src/pocketmine/event/player/PlayerChatEvent.php b/src/pocketmine/event/player/PlayerChatEvent.php
index b12fa0858a..ca54c1a5d1 100644
--- a/src/pocketmine/event/player/PlayerChatEvent.php
+++ b/src/pocketmine/event/player/PlayerChatEvent.php
@@ -52,7 +52,7 @@ class PlayerChatEvent extends PlayerEvent implements Cancellable{
 	 * @param string   $format
 	 * @param Player[] $recipients
 	 */
-	public function __construct(Player $player, string $message, string $format = "chat.type.text", array $recipients = null){
+	public function __construct(Player $player, string $message, string $format = "chat.type.text", ?array $recipients = null){
 		$this->player = $player;
 		$this->message = $message;
 
diff --git a/src/pocketmine/inventory/BaseInventory.php b/src/pocketmine/inventory/BaseInventory.php
index 974ba3b26d..17fe9e66c8 100644
--- a/src/pocketmine/inventory/BaseInventory.php
+++ b/src/pocketmine/inventory/BaseInventory.php
@@ -57,7 +57,7 @@ abstract class BaseInventory implements Inventory{
 	 * @param int    $size
 	 * @param string $title
 	 */
-	public function __construct(array $items = [], int $size = null, string $title = null){
+	public function __construct(array $items = [], ?int $size = null, ?string $title = null){
 		$this->slots = new \SplFixedArray($size ?? $this->getDefaultSize());
 		$this->title = $title ?? $this->getName();
 
diff --git a/src/pocketmine/inventory/ContainerInventory.php b/src/pocketmine/inventory/ContainerInventory.php
index 4ede6d8263..b807b0b08f 100644
--- a/src/pocketmine/inventory/ContainerInventory.php
+++ b/src/pocketmine/inventory/ContainerInventory.php
@@ -33,7 +33,7 @@ abstract class ContainerInventory extends BaseInventory{
 	/** @var Vector3 */
 	protected $holder;
 
-	public function __construct(Vector3 $holder, array $items = [], int $size = null, string $title = null){
+	public function __construct(Vector3 $holder, array $items = [], ?int $size = null, ?string $title = null){
 		$this->holder = $holder;
 		parent::__construct($items, $size, $title);
 	}
diff --git a/src/pocketmine/item/ItemBlock.php b/src/pocketmine/item/ItemBlock.php
index a0c4375f58..e88576026b 100644
--- a/src/pocketmine/item/ItemBlock.php
+++ b/src/pocketmine/item/ItemBlock.php
@@ -38,7 +38,7 @@ class ItemBlock extends Item{
 	 * @param int      $meta usually 0-15 (placed blocks may only have meta values 0-15)
 	 * @param int|null $itemId
 	 */
-	public function __construct(int $blockId, int $meta = 0, int $itemId = null){
+	public function __construct(int $blockId, int $meta = 0, ?int $itemId = null){
 		if($blockId < 0){ //extended blocks
 			if($itemId === null){
 				$itemId = $blockId;
diff --git a/src/pocketmine/lang/Language.php b/src/pocketmine/lang/Language.php
index 05efd6e5a3..13c1b228f5 100644
--- a/src/pocketmine/lang/Language.php
+++ b/src/pocketmine/lang/Language.php
@@ -94,7 +94,7 @@ class Language{
 	 *
 	 * @throws LanguageNotFoundException
 	 */
-	public function __construct(string $lang, string $path = null, string $fallback = self::FALLBACK_LANGUAGE){
+	public function __construct(string $lang, ?string $path = null, string $fallback = self::FALLBACK_LANGUAGE){
 		$this->langName = strtolower($lang);
 
 		if($path === null){
@@ -129,7 +129,7 @@ class Language{
 	 *
 	 * @return string
 	 */
-	public function translateString(string $str, array $params = [], string $onlyPrefix = null) : string{
+	public function translateString(string $str, array $params = [], ?string $onlyPrefix = null) : string{
 		$baseText = $this->get($str);
 		$baseText = $this->parseTranslation(($baseText !== null and ($onlyPrefix === null or strpos($str, $onlyPrefix) === 0)) ? $baseText : $str, $onlyPrefix);
 
@@ -179,7 +179,7 @@ class Language{
 	 *
 	 * @return string
 	 */
-	protected function parseTranslation(string $text, string $onlyPrefix = null) : string{
+	protected function parseTranslation(string $text, ?string $onlyPrefix = null) : string{
 		$newString = "";
 
 		$replaceString = null;
diff --git a/src/pocketmine/level/Level.php b/src/pocketmine/level/Level.php
index 61b5cb8681..40981b0f17 100644
--- a/src/pocketmine/level/Level.php
+++ b/src/pocketmine/level/Level.php
@@ -478,7 +478,7 @@ class Level implements ChunkManager, Metadatable{
 		$this->closed = true;
 	}
 
-	public function addSound(Vector3 $pos, Sound $sound, array $players = null){
+	public function addSound(Vector3 $pos, Sound $sound, ?array $players = null){
 		$pk = $sound->encode($pos);
 		if(!is_array($pk)){
 			$pk = [$pk];
@@ -494,7 +494,7 @@ class Level implements ChunkManager, Metadatable{
 		}
 	}
 
-	public function addParticle(Vector3 $pos, Particle $particle, array $players = null){
+	public function addParticle(Vector3 $pos, Particle $particle, ?array $players = null){
 		$pk = $particle->encode($pos);
 		if(!is_array($pk)){
 			$pk = [$pk];
@@ -1626,7 +1626,7 @@ class Level implements ChunkManager, Metadatable{
 	 *
 	 * @return ItemEntity|null
 	 */
-	public function dropItem(Vector3 $source, Item $item, Vector3 $motion = null, int $delay = 10){
+	public function dropItem(Vector3 $source, Item $item, ?Vector3 $motion = null, int $delay = 10){
 		$motion = $motion ?? new Vector3(lcg_value() * 0.2 - 0.1, 0.2, lcg_value() * 0.2 - 0.1);
 		$itemTag = $item->nbtSerialize();
 		$itemTag->setName("Item");
@@ -1686,7 +1686,7 @@ class Level implements ChunkManager, Metadatable{
 	 *
 	 * @return bool
 	 */
-	public function useBreakOn(Vector3 $vector, Item &$item = null, Player $player = null, bool $createParticles = false) : bool{
+	public function useBreakOn(Vector3 $vector, Item &$item = null, ?Player $player = null, bool $createParticles = false) : bool{
 		$target = $this->getBlock($vector);
 		$affectedBlocks = $target->getAffectedBlocks();
 
@@ -1788,7 +1788,7 @@ class Level implements ChunkManager, Metadatable{
 	 *
 	 * @return bool
 	 */
-	public function useItemOn(Vector3 $vector, Item &$item, int $face, Vector3 $clickVector = null, Player $player = null, bool $playSound = false) : bool{
+	public function useItemOn(Vector3 $vector, Item &$item, int $face, ?Vector3 $clickVector = null, ?Player $player = null, bool $playSound = false) : bool{
 		$blockClicked = $this->getBlock($vector);
 		$blockReplace = $blockClicked->getSide($face);
 
@@ -1928,7 +1928,7 @@ class Level implements ChunkManager, Metadatable{
 	 *
 	 * @return Entity[]
 	 */
-	public function getCollidingEntities(AxisAlignedBB $bb, Entity $entity = null) : array{
+	public function getCollidingEntities(AxisAlignedBB $bb, ?Entity $entity = null) : array{
 		$nearby = [];
 
 		if($entity === null or $entity->canCollide){
@@ -1960,7 +1960,7 @@ class Level implements ChunkManager, Metadatable{
 	 *
 	 * @return Entity[]
 	 */
-	public function getNearbyEntities(AxisAlignedBB $bb, Entity $entity = null) : array{
+	public function getNearbyEntities(AxisAlignedBB $bb, ?Entity $entity = null) : array{
 		$nearby = [];
 
 		$minX = ((int) floor($bb->minX - 2)) >> 4;
diff --git a/src/pocketmine/level/LevelManager.php b/src/pocketmine/level/LevelManager.php
index 2dbbdb1151..6ac55a4163 100644
--- a/src/pocketmine/level/LevelManager.php
+++ b/src/pocketmine/level/LevelManager.php
@@ -259,7 +259,7 @@ class LevelManager{
 	 * @return bool
 	 * @throws \InvalidArgumentException
 	 */
-	public function generateLevel(string $name, int $seed = null, string $generator = Normal::class, array $options = [], bool $backgroundGeneration = true) : bool{
+	public function generateLevel(string $name, ?int $seed = null, string $generator = Normal::class, array $options = [], bool $backgroundGeneration = true) : bool{
 		if(trim($name) === "" or $this->isLevelGenerated($name)){
 			return false;
 		}
diff --git a/src/pocketmine/level/Location.php b/src/pocketmine/level/Location.php
index b24d902421..beb129ef45 100644
--- a/src/pocketmine/level/Location.php
+++ b/src/pocketmine/level/Location.php
@@ -40,7 +40,7 @@ class Location extends Position{
 	 * @param float $pitch
 	 * @param Level $level
 	 */
-	public function __construct($x = 0, $y = 0, $z = 0, $yaw = 0.0, $pitch = 0.0, Level $level = null){
+	public function __construct($x = 0, $y = 0, $z = 0, $yaw = 0.0, $pitch = 0.0, ?Level $level = null){
 		$this->yaw = $yaw;
 		$this->pitch = $pitch;
 		parent::__construct($x, $y, $z, $level);
@@ -54,7 +54,7 @@ class Location extends Position{
 	 *
 	 * @return Location
 	 */
-	public static function fromObject(Vector3 $pos, Level $level = null, $yaw = 0.0, $pitch = 0.0) : Location{
+	public static function fromObject(Vector3 $pos, ?Level $level = null, $yaw = 0.0, $pitch = 0.0) : Location{
 		return new Location($pos->x, $pos->y, $pos->z, $yaw, $pitch, $level ?? (($pos instanceof Position) ? $pos->level : null));
 	}
 
diff --git a/src/pocketmine/level/Position.php b/src/pocketmine/level/Position.php
index b1de803aeb..a6bb3ef67a 100644
--- a/src/pocketmine/level/Position.php
+++ b/src/pocketmine/level/Position.php
@@ -37,12 +37,12 @@ class Position extends Vector3{
 	 * @param int   $z
 	 * @param Level $level
 	 */
-	public function __construct($x = 0, $y = 0, $z = 0, Level $level = null){
+	public function __construct($x = 0, $y = 0, $z = 0, ?Level $level = null){
 		parent::__construct($x, $y, $z);
 		$this->setLevel($level);
 	}
 
-	public static function fromObject(Vector3 $pos, Level $level = null){
+	public static function fromObject(Vector3 $pos, ?Level $level = null){
 		return new Position($pos->x, $pos->y, $pos->z, $level);
 	}
 
diff --git a/src/pocketmine/permission/BanList.php b/src/pocketmine/permission/BanList.php
index df849c1c90..82493e1bf2 100644
--- a/src/pocketmine/permission/BanList.php
+++ b/src/pocketmine/permission/BanList.php
@@ -118,7 +118,7 @@ class BanList{
 	 *
 	 * @return BanEntry
 	 */
-	public function addBan(string $target, string $reason = null, \DateTime $expires = null, string $source = null) : BanEntry{
+	public function addBan(string $target, ?string $reason = null, ?\DateTime $expires = null, ?string $source = null) : BanEntry{
 		$entry = new BanEntry($target);
 		$entry->setSource($source ?? $entry->getSource());
 		$entry->setExpires($expires);
diff --git a/src/pocketmine/permission/DefaultPermissions.php b/src/pocketmine/permission/DefaultPermissions.php
index 465f7a7754..015f87d54f 100644
--- a/src/pocketmine/permission/DefaultPermissions.php
+++ b/src/pocketmine/permission/DefaultPermissions.php
@@ -35,7 +35,7 @@ abstract class DefaultPermissions{
 	 *
 	 * @return Permission
 	 */
-	public static function registerPermission(Permission $perm, Permission $parent = null) : Permission{
+	public static function registerPermission(Permission $perm, ?Permission $parent = null) : Permission{
 		if($parent instanceof Permission){
 			$parent->getChildren()[$perm->getName()] = true;
 
diff --git a/src/pocketmine/permission/Permissible.php b/src/pocketmine/permission/Permissible.php
index 517750cacc..21ebba7b2c 100644
--- a/src/pocketmine/permission/Permissible.php
+++ b/src/pocketmine/permission/Permissible.php
@@ -52,7 +52,7 @@ interface Permissible extends ServerOperator{
 	 *
 	 * @return PermissionAttachment
 	 */
-	public function addAttachment(Plugin $plugin, string $name = null, bool $value = null) : PermissionAttachment;
+	public function addAttachment(Plugin $plugin, ?string $name = null, ?bool $value = null) : PermissionAttachment;
 
 	/**
 	 * @param PermissionAttachment $attachment
diff --git a/src/pocketmine/permission/PermissibleBase.php b/src/pocketmine/permission/PermissibleBase.php
index 809d62c756..47b5acfde5 100644
--- a/src/pocketmine/permission/PermissibleBase.php
+++ b/src/pocketmine/permission/PermissibleBase.php
@@ -111,7 +111,7 @@ class PermissibleBase implements Permissible{
 	 *
 	 * @return PermissionAttachment
 	 */
-	public function addAttachment(Plugin $plugin, string $name = null, bool $value = null) : PermissionAttachment{
+	public function addAttachment(Plugin $plugin, ?string $name = null, ?bool $value = null) : PermissionAttachment{
 		if(!$plugin->isEnabled()){
 			throw new PluginException("Plugin " . $plugin->getDescription()->getName() . " is disabled");
 		}
diff --git a/src/pocketmine/permission/Permission.php b/src/pocketmine/permission/Permission.php
index 9bbd374e56..4759d0666a 100644
--- a/src/pocketmine/permission/Permission.php
+++ b/src/pocketmine/permission/Permission.php
@@ -60,7 +60,7 @@ class Permission{
 	 * @param string $defaultValue
 	 * @param bool[] $children
 	 */
-	public function __construct(string $name, string $description = null, string $defaultValue = null, array $children = []){
+	public function __construct(string $name, ?string $description = null, ?string $defaultValue = null, array $children = []){
 		$this->name = $name;
 		$this->description = $description ?? "";
 		$this->defaultValue = $defaultValue ?? self::$DEFAULT_PERMISSION;
diff --git a/src/pocketmine/plugin/PluginManager.php b/src/pocketmine/plugin/PluginManager.php
index 3e7e1270f5..93f4c4edc6 100644
--- a/src/pocketmine/plugin/PluginManager.php
+++ b/src/pocketmine/plugin/PluginManager.php
@@ -137,7 +137,7 @@ class PluginManager{
 	 *
 	 * @return Plugin|null
 	 */
-	public function loadPlugin(string $path, array $loaders = null) : ?Plugin{
+	public function loadPlugin(string $path, ?array $loaders = null) : ?Plugin{
 		foreach($loaders ?? $this->fileAssociations as $loader){
 			if($loader->canLoadPlugin($path)){
 				$description = $loader->getPluginDescription($path);
@@ -193,7 +193,7 @@ class PluginManager{
 	 *
 	 * @return Plugin[]
 	 */
-	public function loadPlugins(string $directory, array $newLoaders = null){
+	public function loadPlugins(string $directory, ?array $newLoaders = null){
 		if(!is_dir($directory)){
 			return [];
 		}
diff --git a/src/pocketmine/timings/TimingsHandler.php b/src/pocketmine/timings/TimingsHandler.php
index 102f5466cc..8889e2b142 100644
--- a/src/pocketmine/timings/TimingsHandler.php
+++ b/src/pocketmine/timings/TimingsHandler.php
@@ -150,7 +150,7 @@ class TimingsHandler{
 	 * @param string         $name
 	 * @param TimingsHandler $parent
 	 */
-	public function __construct(string $name, TimingsHandler $parent = null){
+	public function __construct(string $name, ?TimingsHandler $parent = null){
 		$this->name = $name;
 		$this->parent = $parent;
 
diff --git a/src/pocketmine/utils/Internet.php b/src/pocketmine/utils/Internet.php
index ebd704bdaa..b7f9ab1cf0 100644
--- a/src/pocketmine/utils/Internet.php
+++ b/src/pocketmine/utils/Internet.php
@@ -193,7 +193,7 @@ class Internet{
 	 *
 	 * @throws InternetException if a cURL error occurs
 	 */
-	public static function simpleCurl(string $page, $timeout = 10, array $extraHeaders = [], array $extraOpts = [], callable $onSuccess = null){
+	public static function simpleCurl(string $page, $timeout = 10, array $extraHeaders = [], array $extraOpts = [], ?callable $onSuccess = null){
 		if(!self::$online){
 			throw new InternetException("Cannot execute web request while offline");
 		}
diff --git a/src/pocketmine/utils/UUID.php b/src/pocketmine/utils/UUID.php
index 0c21d8a7b8..703d9fdc74 100644
--- a/src/pocketmine/utils/UUID.php
+++ b/src/pocketmine/utils/UUID.php
@@ -41,7 +41,7 @@ class UUID{
 	private $parts = [0, 0, 0, 0];
 	private $version = null;
 
-	public function __construct(int $part1 = 0, int $part2 = 0, int $part3 = 0, int $part4 = 0, int $version = null){
+	public function __construct(int $part1 = 0, int $part2 = 0, int $part3 = 0, int $part4 = 0, ?int $version = null){
 		$this->parts = [$part1, $part2, $part3, $part4];
 
 		$this->version = $version ?? ($this->parts[1] & 0xf000) >> 12;
@@ -63,7 +63,7 @@ class UUID{
 	 *
 	 * @return UUID
 	 */
-	public static function fromString(string $uuid, int $version = null) : UUID{
+	public static function fromString(string $uuid, ?int $version = null) : UUID{
 		return self::fromBinary(hex2bin(str_replace("-", "", trim($uuid))), $version);
 	}
 
@@ -77,7 +77,7 @@ class UUID{
 	 *
 	 * @throws \InvalidArgumentException
 	 */
-	public static function fromBinary(string $uuid, int $version = null) : UUID{
+	public static function fromBinary(string $uuid, ?int $version = null) : UUID{
 		if(strlen($uuid) !== 16){
 			throw new \InvalidArgumentException("Must have exactly 16 bytes");
 		}