diff --git a/.gitignore b/.gitignore
index b1a8308b6..be3b46bfa 100644
--- a/.gitignore
+++ b/.gitignore
@@ -53,3 +53,6 @@ gradle-app.setting
 
 # When running the demo we generate the extensions folder
 /extensions/
+
+# When compiling we get a docs folder
+/docs
\ No newline at end of file
diff --git a/src/generators/java/net/minestom/codegen/blocks/BlockEnumGenerator.java b/src/generators/java/net/minestom/codegen/blocks/BlockEnumGenerator.java
index 9b9eb8fb8..7b519b96e 100644
--- a/src/generators/java/net/minestom/codegen/blocks/BlockEnumGenerator.java
+++ b/src/generators/java/net/minestom/codegen/blocks/BlockEnumGenerator.java
@@ -35,7 +35,7 @@ public class BlockEnumGenerator extends MinestomEnumGenerator<BlockContainer> {
     private final String targetVersion;
     private final File targetFolder;
 
-    private CodeBlock.Builder staticBlock = CodeBlock.builder();
+    private final CodeBlock.Builder staticBlock = CodeBlock.builder();
 
 
     public static void main(String[] args) throws IOException {
@@ -161,8 +161,6 @@ public class BlockEnumGenerator extends MinestomEnumGenerator<BlockContainer> {
             }
 
             return blocks;
-        } catch (IOException e) {
-            throw e;
         }
     }
 
@@ -178,8 +176,6 @@ public class BlockEnumGenerator extends MinestomEnumGenerator<BlockContainer> {
         try (BufferedReader bufferedReader = new BufferedReader(new FileReader(blockFile))) {
             PrismarineJSBlock[] blocks = gson.fromJson(bufferedReader, PrismarineJSBlock[].class);
             return Arrays.asList(blocks);
-        } catch (IOException e) {
-            throw e;
         }
     }
 
diff --git a/src/generators/java/net/minestom/codegen/items/ItemEnumGenerator.java b/src/generators/java/net/minestom/codegen/items/ItemEnumGenerator.java
index ab3900ece..4b4f44053 100644
--- a/src/generators/java/net/minestom/codegen/items/ItemEnumGenerator.java
+++ b/src/generators/java/net/minestom/codegen/items/ItemEnumGenerator.java
@@ -85,8 +85,6 @@ public class ItemEnumGenerator extends MinestomEnumGenerator<ItemContainer> {
                 items.add(item);
             }
             return items;
-        } catch (IOException e) {
-            throw e;
         }
     }
 
diff --git a/src/lwjgl/java/net/minestom/server/map/PaletteGenerator.java b/src/lwjgl/java/net/minestom/server/map/PaletteGenerator.java
index 9f6e2f413..cb3de987b 100644
--- a/src/lwjgl/java/net/minestom/server/map/PaletteGenerator.java
+++ b/src/lwjgl/java/net/minestom/server/map/PaletteGenerator.java
@@ -1,5 +1,8 @@
 package net.minestom.server.map;
 
+import it.unimi.dsi.fastutil.ints.Int2IntMap;
+import it.unimi.dsi.fastutil.ints.Int2IntOpenHashMap;
+
 import javax.imageio.ImageIO;
 import java.awt.image.BufferedImage;
 import java.io.File;
@@ -10,7 +13,7 @@ import java.util.Map;
 public class PaletteGenerator {
 
     public static void main(String[] args) {
-        Map<Integer, Integer> colors = new HashMap<>();
+        Int2IntMap colors = new Int2IntOpenHashMap();
         int highestIndex = 0;
         for(MapColors c : MapColors.values()) {
             if (c == MapColors.NONE)
diff --git a/src/main/java/net/minestom/server/MinecraftServer.java b/src/main/java/net/minestom/server/MinecraftServer.java
index 553c6095f..f366fb19c 100644
--- a/src/main/java/net/minestom/server/MinecraftServer.java
+++ b/src/main/java/net/minestom/server/MinecraftServer.java
@@ -217,7 +217,6 @@ public final class MinecraftServer {
      * @throws NullPointerException if {@code brandName} is null
      */
     public static void setBrandName(@NotNull String brandName) {
-        Check.notNull(brandName, "The brand name cannot be null");
         MinecraftServer.brandName = brandName;
 
         PacketUtils.sendGroupedPacket(connectionManager.getOnlinePlayers(), PluginMessagePacket.getBrandPacket());
@@ -275,7 +274,6 @@ public final class MinecraftServer {
      * @param difficulty the new server difficulty
      */
     public static void setDifficulty(@NotNull Difficulty difficulty) {
-        Check.notNull(difficulty, "The server difficulty cannot be null.");
         MinecraftServer.difficulty = difficulty;
 
         // Send the packet to all online players
@@ -478,9 +476,7 @@ public final class MinecraftServer {
         MinecraftServer.chunkViewDistance = chunkViewDistance;
         if (started) {
 
-            final Collection<Player> players = connectionManager.getOnlinePlayers();
-
-            players.forEach(player -> {
+            for (final Player player : connectionManager.getOnlinePlayers()) {
                 final Chunk playerChunk = player.getChunk();
                 if (playerChunk != null) {
 
@@ -490,7 +486,7 @@ public final class MinecraftServer {
 
                     player.refreshVisibleChunks(playerChunk);
                 }
-            });
+            }
         }
     }
 
@@ -514,12 +510,12 @@ public final class MinecraftServer {
                 "The entity view distance must be between 0 and 32");
         MinecraftServer.entityViewDistance = entityViewDistance;
         if (started) {
-            connectionManager.getOnlinePlayers().forEach(player -> {
+            for (final Player player : connectionManager.getOnlinePlayers()) {
                 final Chunk playerChunk = player.getChunk();
                 if (playerChunk != null) {
                     player.refreshVisibleEntities(playerChunk);
                 }
-            });
+            }
         }
     }
 
diff --git a/src/main/java/net/minestom/server/UpdateManager.java b/src/main/java/net/minestom/server/UpdateManager.java
index 6b546efca..ef22e6987 100644
--- a/src/main/java/net/minestom/server/UpdateManager.java
+++ b/src/main/java/net/minestom/server/UpdateManager.java
@@ -140,7 +140,6 @@ public final class UpdateManager {
      * @throws NullPointerException if <code>threadProvider</code> is null
      */
     public synchronized void setThreadProvider(ThreadProvider threadProvider) {
-        Check.notNull(threadProvider, "The thread provider cannot be null");
         this.threadProvider = threadProvider;
     }
 
diff --git a/src/main/java/net/minestom/server/advancements/AdvancementTab.java b/src/main/java/net/minestom/server/advancements/AdvancementTab.java
index 67515f0c6..5bc96795b 100644
--- a/src/main/java/net/minestom/server/advancements/AdvancementTab.java
+++ b/src/main/java/net/minestom/server/advancements/AdvancementTab.java
@@ -73,7 +73,6 @@ public class AdvancementTab implements Viewable {
      * @param parent      the parent of this advancement, it cannot be null
      */
     public void createAdvancement(@NotNull String identifier, @NotNull Advancement advancement, @NotNull Advancement parent) {
-        Check.argCondition(identifier == null, "the advancement identifier cannot be null");
         Check.stateCondition(!advancementMap.containsKey(parent),
                 "You tried to set a parent which doesn't exist or isn't registered");
         cacheAdvancement(identifier, advancement, parent);
diff --git a/src/main/java/net/minestom/server/chat/ColoredText.java b/src/main/java/net/minestom/server/chat/ColoredText.java
index 394780a6e..dabdd1ea3 100644
--- a/src/main/java/net/minestom/server/chat/ColoredText.java
+++ b/src/main/java/net/minestom/server/chat/ColoredText.java
@@ -19,8 +19,11 @@ import java.util.regex.Pattern;
  */
 public class ColoredText extends JsonMessage {
 
-    // the raw text
-    private String message;
+    /**
+     * The raw text StringBuilder
+     * Its a single StringBuilder instance for easier and faster concenation
+     */
+    private final StringBuilder message = new StringBuilder();
 
     /**
      * Creates a colored text.
@@ -31,7 +34,7 @@ public class ColoredText extends JsonMessage {
      * @see #of(String) to create a colored text
      */
     private ColoredText(@NotNull String message) {
-        this.message = message;
+        this.message.append(message);
         refreshUpdate();
     }
 
@@ -79,7 +82,7 @@ public class ColoredText extends JsonMessage {
      */
     @NotNull
     public ColoredText append(@NotNull ChatColor color, @NotNull String message) {
-        this.message += color + message;
+        this.message.append(color).append(message);
         refreshUpdate();
         return this;
     }
@@ -116,7 +119,7 @@ public class ColoredText extends JsonMessage {
      */
     @NotNull
     public String getMessage() {
-        return message;
+        return message.toString();
     }
 
     /**
@@ -160,7 +163,7 @@ public class ColoredText extends JsonMessage {
     protected List<JsonObject> getComponents() {
         final List<JsonObject> objects = new ArrayList<>();
         // No message, return empty list
-        if (message.isEmpty())
+        if (getMessage().isEmpty())
             return objects;
 
         boolean inFormat = false;
diff --git a/src/main/java/net/minestom/server/chat/RichMessage.java b/src/main/java/net/minestom/server/chat/RichMessage.java
index b260208a1..97a3e4d0a 100644
--- a/src/main/java/net/minestom/server/chat/RichMessage.java
+++ b/src/main/java/net/minestom/server/chat/RichMessage.java
@@ -37,7 +37,6 @@ public class RichMessage extends JsonMessage {
      * @return the created rich message object
      */
     public static RichMessage of(@NotNull ColoredText coloredText) {
-        Check.notNull(coloredText, "ColoredText cannot be null");
 
         RichMessage richMessage = new RichMessage();
         appendText(richMessage, coloredText);
@@ -58,7 +57,6 @@ public class RichMessage extends JsonMessage {
      * @return the rich message
      */
     public RichMessage append(@NotNull ColoredText coloredText) {
-        Check.notNull(coloredText, "ColoredText cannot be null");
 
         appendText(this, coloredText);
         return this;
diff --git a/src/main/java/net/minestom/server/command/CommandManager.java b/src/main/java/net/minestom/server/command/CommandManager.java
index 4fe28836c..e42bbd0d9 100644
--- a/src/main/java/net/minestom/server/command/CommandManager.java
+++ b/src/main/java/net/minestom/server/command/CommandManager.java
@@ -185,8 +185,6 @@ public final class CommandManager {
      * @return true if the command hadn't been cancelled and has been successful
      */
     public boolean execute(@NotNull CommandSender sender, @NotNull String command) {
-        Check.notNull(sender, "Source cannot be null");
-        Check.notNull(command, "Command string cannot be null");
 
         // Command event
         if (sender instanceof Player) {
diff --git a/src/main/java/net/minestom/server/command/CommandSender.java b/src/main/java/net/minestom/server/command/CommandSender.java
index d2cfea6db..a5f928af2 100644
--- a/src/main/java/net/minestom/server/command/CommandSender.java
+++ b/src/main/java/net/minestom/server/command/CommandSender.java
@@ -39,7 +39,7 @@ public interface CommandSender extends PermissionHandler {
      * */
     default void sendMessage(@NotNull JsonMessage text) {
         if (this instanceof Player) {
-            ((Player) this).sendMessage((JsonMessage) text);
+            this.sendMessage(text);
         } else {
             sendMessage(text.getRawMessage());
         }
diff --git a/src/main/java/net/minestom/server/command/builder/CommandDispatcher.java b/src/main/java/net/minestom/server/command/builder/CommandDispatcher.java
index d027b2d4e..90fdaa85e 100644
--- a/src/main/java/net/minestom/server/command/builder/CommandDispatcher.java
+++ b/src/main/java/net/minestom/server/command/builder/CommandDispatcher.java
@@ -1,5 +1,6 @@
 package net.minestom.server.command.builder;
 
+import it.unimi.dsi.fastutil.ints.Int2ObjectRBTreeMap;
 import net.minestom.server.command.CommandSender;
 import net.minestom.server.command.builder.arguments.Argument;
 import net.minestom.server.command.builder.condition.CommandCondition;
@@ -58,6 +59,7 @@ public class CommandDispatcher {
      * @param commandString the command (containing the command name and the args if any)
      * @return the result of the parsing, null if the command doesn't exist
      */
+    @Nullable
     public CommandResult parse(@NotNull String commandString) {
         commandString = commandString.trim();
 
@@ -131,7 +133,7 @@ public class CommandDispatcher {
 
         // Contains all the syntaxes that are not fully correct, used to later, retrieve the "most correct syntax"
         // Number of correct argument - The data about the failing argument
-        TreeMap<Integer, CommandSuggestionHolder> syntaxesSuggestions = new TreeMap<>(Collections.reverseOrder());
+        Int2ObjectRBTreeMap<CommandSuggestionHolder> syntaxesSuggestions = new Int2ObjectRBTreeMap<>(Collections.reverseOrder());
 
         for (CommandSyntax syntax : syntaxes) {
             final Argument<?>[] arguments = syntax.getArguments();
@@ -257,7 +259,7 @@ public class CommandDispatcher {
         {
             // Get closest valid syntax
             if (!syntaxesSuggestions.isEmpty()) {
-                final int max = syntaxesSuggestions.firstKey(); // number of correct arguments in the most correct syntax
+                final int max = syntaxesSuggestions.firstIntKey(); // number of correct arguments in the most correct syntax
                 final CommandSuggestionHolder suggestionHolder = syntaxesSuggestions.get(max);
                 final CommandSyntax syntax = suggestionHolder.syntax;
                 final ArgumentSyntaxException argumentSyntaxException = suggestionHolder.argumentSyntaxException;
diff --git a/src/main/java/net/minestom/server/entity/Entity.java b/src/main/java/net/minestom/server/entity/Entity.java
index 910ebb26c..0f817882c 100644
--- a/src/main/java/net/minestom/server/entity/Entity.java
+++ b/src/main/java/net/minestom/server/entity/Entity.java
@@ -242,7 +242,6 @@ public abstract class Entity implements Viewable, EventHandler, DataContainer, P
      * @throws IllegalStateException if you try to teleport an entity before settings its instance
      */
     public void teleport(@NotNull Position position, @Nullable long[] chunks, @Nullable Runnable callback) {
-        Check.notNull(position, "Teleport position cannot be null");
         Check.stateCondition(instance == null, "You need to use Entity#setInstance before teleporting an entity!");
 
         final ChunkCallback endCallback = (chunk) -> {
@@ -329,7 +328,6 @@ public abstract class Entity implements Viewable, EventHandler, DataContainer, P
 
     @Override
     public boolean addViewer(@NotNull Player player) {
-        Check.notNull(player, "Viewer cannot be null");
         boolean result = this.viewers.add(player);
         if (!result)
             return false;
@@ -339,7 +337,6 @@ public abstract class Entity implements Viewable, EventHandler, DataContainer, P
 
     @Override
     public boolean removeViewer(@NotNull Player player) {
-        Check.notNull(player, "Viewer cannot be null");
         if (!viewers.remove(player))
             return false;
 
@@ -757,7 +754,6 @@ public abstract class Entity implements Viewable, EventHandler, DataContainer, P
      * @throws IllegalStateException if {@code instance} has not been registered in {@link InstanceManager}
      */
     public void setInstance(@NotNull Instance instance) {
-        Check.notNull(instance, "instance cannot be null!");
         Check.stateCondition(!instance.isRegistered(),
                 "Instances need to be registered, please use InstanceManager#registerInstance or InstanceManager#registerSharedInstance");
 
@@ -866,7 +862,6 @@ public abstract class Entity implements Viewable, EventHandler, DataContainer, P
      * @return the distance between this and {@code entity}
      */
     public float getDistance(@NotNull Entity entity) {
-        Check.notNull(entity, "Entity cannot be null");
         return getPosition().getDistance(entity.getPosition());
     }
 
@@ -888,7 +883,6 @@ public abstract class Entity implements Viewable, EventHandler, DataContainer, P
      * @throws IllegalStateException if {@link #getInstance()} returns null
      */
     public void addPassenger(@NotNull Entity entity) {
-        Check.notNull(entity, "Passenger cannot be null");
         Check.stateCondition(instance == null, "You need to set an instance using Entity#setInstance");
 
         if (entity.getVehicle() != null) {
@@ -909,7 +903,6 @@ public abstract class Entity implements Viewable, EventHandler, DataContainer, P
      * @throws IllegalStateException if {@link #getInstance()} returns null
      */
     public void removePassenger(@NotNull Entity entity) {
-        Check.notNull(entity, "Passenger cannot be null");
         Check.stateCondition(instance == null, "You need to set an instance using Entity#setInstance");
 
         if (!passengers.remove(entity))
diff --git a/src/main/java/net/minestom/server/entity/LivingEntity.java b/src/main/java/net/minestom/server/entity/LivingEntity.java
index 8ace0671d..82d8e4bf6 100644
--- a/src/main/java/net/minestom/server/entity/LivingEntity.java
+++ b/src/main/java/net/minestom/server/entity/LivingEntity.java
@@ -272,7 +272,6 @@ public abstract class LivingEntity extends Entity implements EquipmentHandler {
      * @return true if damage has been applied, false if it didn't
      */
     public boolean damage(@NotNull DamageType type, float value) {
-        Check.notNull(type, "The damage type cannot be null!");
         if (isDead())
             return false;
         if (isInvulnerable() || isImmune(type)) {
diff --git a/src/main/java/net/minestom/server/entity/Player.java b/src/main/java/net/minestom/server/entity/Player.java
index 4925ced5c..ba2ce704e 100644
--- a/src/main/java/net/minestom/server/entity/Player.java
+++ b/src/main/java/net/minestom/server/entity/Player.java
@@ -536,7 +536,7 @@ public class Player extends LivingEntity implements CommandSender {
 
             // #buildDeathScreenText can return null, check here
             if (deathText != null) {
-                CombatEventPacket deathPacket = CombatEventPacket.death(this, Optional.empty(), deathText);
+                CombatEventPacket deathPacket = CombatEventPacket.death(this, null, deathText);
                 playerConnection.sendPacket(deathPacket);
             }
 
@@ -670,7 +670,6 @@ public class Player extends LivingEntity implements CommandSender {
      * @param spawnPosition the new position of the player
      */
     public void setInstance(@NotNull Instance instance, @NotNull Position spawnPosition) {
-        Check.notNull(instance, "instance cannot be null!");
         Check.argCondition(this.instance == instance, "Instance should be different than the current one");
 
         // true if the chunks need to be sent to the client, can be false if the instances share the same chunks (eg SharedInstance)
@@ -1364,7 +1363,6 @@ public class Player extends LivingEntity implements CommandSender {
      * @param resourcePack the resource pack
      */
     public void setResourcePack(@NotNull ResourcePack resourcePack) {
-        Check.notNull(resourcePack, "The resource pack cannot be null");
         final String url = resourcePack.getUrl();
         final String hash = resourcePack.getHash();
 
@@ -1737,7 +1735,6 @@ public class Player extends LivingEntity implements CommandSender {
      * @param gameMode the new player GameMode
      */
     public void setGameMode(@NotNull GameMode gameMode) {
-        Check.notNull(gameMode, "GameMode cannot be null");
         this.gameMode = gameMode;
 
         // Condition to prevent sending the packets before spawning the player
@@ -1766,7 +1763,6 @@ public class Player extends LivingEntity implements CommandSender {
      * @param dimensionType the new player dimension
      */
     protected void sendDimension(@NotNull DimensionType dimensionType) {
-        Check.notNull(dimensionType, "Dimension cannot be null!");
         Check.argCondition(dimensionType.equals(getDimensionType()), "The dimension needs to be different than the current one!");
 
         this.dimensionType = dimensionType;
@@ -1900,7 +1896,6 @@ public class Player extends LivingEntity implements CommandSender {
      * @return true if the inventory has been opened/sent to the player, false otherwise (cancelled by event)
      */
     public boolean openInventory(@NotNull Inventory inventory) {
-        Check.notNull(inventory, "Inventory cannot be null, use Player#closeInventory() to close current");
 
         InventoryOpenEvent inventoryOpenEvent = new InventoryOpenEvent(inventory, this);
 
diff --git a/src/main/java/net/minestom/server/entity/ai/goal/EatBlockGoal.java b/src/main/java/net/minestom/server/entity/ai/goal/EatBlockGoal.java
index 9104590dc..aea57a783 100644
--- a/src/main/java/net/minestom/server/entity/ai/goal/EatBlockGoal.java
+++ b/src/main/java/net/minestom/server/entity/ai/goal/EatBlockGoal.java
@@ -7,7 +7,6 @@ import net.minestom.server.instance.Instance;
 import net.minestom.server.utils.BlockPosition;
 import org.jetbrains.annotations.NotNull;
 
-import java.util.Map;
 import java.util.Random;
 
 public class EatBlockGoal extends GoalSelector {
diff --git a/src/main/java/net/minestom/server/entity/pathfinding/NavigableEntity.java b/src/main/java/net/minestom/server/entity/pathfinding/NavigableEntity.java
index 5e0b21145..0b8f62d16 100644
--- a/src/main/java/net/minestom/server/entity/pathfinding/NavigableEntity.java
+++ b/src/main/java/net/minestom/server/entity/pathfinding/NavigableEntity.java
@@ -30,7 +30,6 @@ public interface NavigableEntity {
      * @param speed     define how far the entity will move
      */
     default void moveTowards(@NotNull Position direction, float speed) {
-        Check.notNull(direction, "The direction cannot be null");
 
         final Position position = getNavigableEntity().getPosition();
 
diff --git a/src/main/java/net/minestom/server/event/handler/EventHandler.java b/src/main/java/net/minestom/server/event/handler/EventHandler.java
index eaec31f87..73a583ff4 100644
--- a/src/main/java/net/minestom/server/event/handler/EventHandler.java
+++ b/src/main/java/net/minestom/server/event/handler/EventHandler.java
@@ -37,8 +37,6 @@ public interface EventHandler {
      * @return true if the callback collection changed as a result of the call
      */
     default <E extends Event> boolean addEventCallback(@NotNull Class<E> eventClass, @NotNull EventCallback<E> eventCallback) {
-        Check.notNull(eventClass, "Event class cannot be null");
-        Check.notNull(eventCallback, "Event callback cannot be null");
         Collection<EventCallback> callbacks = getEventCallbacks(eventClass);
         return callbacks.add(eventCallback);
     }
@@ -52,8 +50,6 @@ public interface EventHandler {
      * @return true if the callback was removed as a result of this call
      */
     default <E extends Event> boolean removeEventCallback(@NotNull Class<E> eventClass, @NotNull EventCallback<E> eventCallback) {
-        Check.notNull(eventClass, "Event class cannot be null");
-        Check.notNull(eventCallback, "Event callback cannot be null");
         Collection<EventCallback> callbacks = getEventCallbacks(eventClass);
         return callbacks.remove(eventCallback);
     }
@@ -67,7 +63,6 @@ public interface EventHandler {
      */
     @NotNull
     default <E extends Event> Collection<EventCallback> getEventCallbacks(@NotNull Class<E> eventClass) {
-        Check.notNull(eventClass, "Event class cannot be null");
         return getEventCallbacksMap().computeIfAbsent(eventClass, clazz -> new CopyOnWriteArraySet<>());
     }
 
diff --git a/src/main/java/net/minestom/server/extras/selfmodification/MinestomExtensionClassLoader.java b/src/main/java/net/minestom/server/extras/selfmodification/MinestomExtensionClassLoader.java
index 7df07b288..6afbee103 100644
--- a/src/main/java/net/minestom/server/extras/selfmodification/MinestomExtensionClassLoader.java
+++ b/src/main/java/net/minestom/server/extras/selfmodification/MinestomExtensionClassLoader.java
@@ -58,8 +58,7 @@ public class MinestomExtensionClassLoader extends HierarchyClassLoader {
         } catch (ClassNotFoundException e) {
             for(MinestomExtensionClassLoader child : children) {
                 try {
-                    Class<?> loaded = child.loadClassAsChild(name, resolve);
-                    return loaded;
+                    return child.loadClassAsChild(name, resolve);
                 } catch (ClassNotFoundException e1) {
                     // move on to next child
                 }
diff --git a/src/main/java/net/minestom/server/instance/BlockModifier.java b/src/main/java/net/minestom/server/instance/BlockModifier.java
index 3cfb2b852..c5a7fdfe2 100644
--- a/src/main/java/net/minestom/server/instance/BlockModifier.java
+++ b/src/main/java/net/minestom/server/instance/BlockModifier.java
@@ -71,13 +71,10 @@ public interface BlockModifier {
     }
 
     default void setBlock(@NotNull BlockPosition blockPosition, @NotNull Block block) {
-        Check.notNull(blockPosition, "The block position cannot be null");
-        Check.notNull(block, "The block cannot be null");
         setBlock(blockPosition.getX(), blockPosition.getY(), blockPosition.getZ(), block);
     }
 
     default void setBlockStateId(@NotNull BlockPosition blockPosition, short blockStateId) {
-        Check.notNull(blockPosition, "The block position cannot be null");
         setBlockStateId(blockPosition.getX(), blockPosition.getY(), blockPosition.getZ(), blockStateId);
     }
 
@@ -97,7 +94,6 @@ public interface BlockModifier {
     }
 
     default void setCustomBlock(@NotNull BlockPosition blockPosition, @NotNull String customBlockId) {
-        Check.notNull(blockPosition, "The block position cannot be null");
         setCustomBlock(blockPosition.getX(), blockPosition.getY(), blockPosition.getZ(), customBlockId);
     }
 
@@ -106,7 +102,6 @@ public interface BlockModifier {
     }
 
     default void setSeparateBlocks(@NotNull BlockPosition blockPosition, short blockStateId, short customBlockId) {
-        Check.notNull(blockPosition, "The block position cannot be null");
         setSeparateBlocks(blockPosition.getX(), blockPosition.getY(), blockPosition.getZ(), blockStateId, customBlockId, null);
     }
 
diff --git a/src/main/java/net/minestom/server/instance/Chunk.java b/src/main/java/net/minestom/server/instance/Chunk.java
index 736091c18..d3e678844 100644
--- a/src/main/java/net/minestom/server/instance/Chunk.java
+++ b/src/main/java/net/minestom/server/instance/Chunk.java
@@ -1,5 +1,6 @@
 package net.minestom.server.instance;
 
+import it.unimi.dsi.fastutil.ints.IntSet;
 import net.minestom.server.MinecraftServer;
 import net.minestom.server.Viewable;
 import net.minestom.server.data.Data;
diff --git a/src/main/java/net/minestom/server/instance/InstanceContainer.java b/src/main/java/net/minestom/server/instance/InstanceContainer.java
index 652f79d9f..f1ca1d782 100644
--- a/src/main/java/net/minestom/server/instance/InstanceContainer.java
+++ b/src/main/java/net/minestom/server/instance/InstanceContainer.java
@@ -508,7 +508,6 @@ public class InstanceContainer extends Instance {
 
     @Override
     public ChunkBatch createChunkBatch(@NotNull Chunk chunk) {
-        Check.notNull(chunk, "The chunk of a ChunkBatch cannot be null");
         return new ChunkBatch(this, chunk, false);
     }
 
@@ -587,7 +586,6 @@ public class InstanceContainer extends Instance {
      * @throws NullPointerException if {@code chunkSupplier} is null
      */
     public void setChunkSupplier(@NotNull ChunkSupplier chunkSupplier) {
-        Check.notNull(chunkSupplier, "The chunk supplier cannot be null!");
         this.chunkSupplier = chunkSupplier;
     }
 
diff --git a/src/main/java/net/minestom/server/inventory/click/InventoryClickProcessor.java b/src/main/java/net/minestom/server/inventory/click/InventoryClickProcessor.java
index 5eeb7d930..949029f78 100644
--- a/src/main/java/net/minestom/server/inventory/click/InventoryClickProcessor.java
+++ b/src/main/java/net/minestom/server/inventory/click/InventoryClickProcessor.java
@@ -19,7 +19,6 @@ import org.jetbrains.annotations.Nullable;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
-import java.util.Set;
 import java.util.function.BiConsumer;
 
 public class InventoryClickProcessor {
@@ -161,12 +160,12 @@ public class InventoryClickProcessor {
             if (cursor.isAir()) {
                 // if held item [key] is air then set clicked to held
                 resultClicked = ItemStack.getAirItem();
-                resultHeld = clicked;
             } else {
                 // Otherwise replace held item and held
                 resultClicked = cursor;
-                resultHeld = clicked;
             }
+
+            resultHeld = clicked;
         }
 
         clickResult.setClicked(resultClicked);
@@ -278,7 +277,7 @@ public class InventoryClickProcessor {
                 // End left
                 if (!leftDraggingMap.containsKey(player))
                     return null;
-                final Set<Integer> slots = leftDraggingMap.get(player);
+                final IntSet slots = leftDraggingMap.get(player);
                 final int slotCount = slots.size();
                 final int cursorAmount = stackingRule.getAmount(cursor);
                 if (slotCount > cursorAmount)
@@ -287,7 +286,7 @@ public class InventoryClickProcessor {
                 final int slotSize = (int) ((float) cursorAmount / (float) slotCount);
                 int finalCursorAmount = cursorAmount;
 
-                for (Integer s : slots) {
+                for (int s : slots) {
                     final ItemStack draggedItem = cursor.clone();
                     ItemStack slotItem = itemGetter.apply(s);
 
@@ -322,12 +321,12 @@ public class InventoryClickProcessor {
                 // End right
                 if (!rightDraggingMap.containsKey(player))
                     return null;
-                final Set<Integer> slots = rightDraggingMap.get(player);
+                final IntSet slots = rightDraggingMap.get(player);
                 final int size = slots.size();
                 int cursorAmount = stackingRule.getAmount(cursor);
                 if (size > cursorAmount)
                     return null;
-                for (Integer s : slots) {
+                for (int s : slots) {
                     ItemStack draggedItem = cursor.clone();
                     ItemStack slotItem = itemGetter.apply(s);
 
diff --git a/src/main/java/net/minestom/server/item/ItemDisplay.java b/src/main/java/net/minestom/server/item/ItemDisplay.java
index eb71fb57f..74344bb75 100644
--- a/src/main/java/net/minestom/server/item/ItemDisplay.java
+++ b/src/main/java/net/minestom/server/item/ItemDisplay.java
@@ -1,6 +1,5 @@
 package net.minestom.server.item;
 
-import net.minestom.server.chat.ColoredText;
 import net.minestom.server.chat.JsonMessage;
 
 public class ItemDisplay {
diff --git a/src/main/java/net/minestom/server/item/ItemStack.java b/src/main/java/net/minestom/server/item/ItemStack.java
index 400339743..b11e94e4e 100644
--- a/src/main/java/net/minestom/server/item/ItemStack.java
+++ b/src/main/java/net/minestom/server/item/ItemStack.java
@@ -1,5 +1,7 @@
 package net.minestom.server.item;
 
+import it.unimi.dsi.fastutil.objects.Object2ShortMap;
+import it.unimi.dsi.fastutil.objects.Object2ShortOpenHashMap;
 import net.minestom.server.chat.JsonMessage;
 import net.minestom.server.data.Data;
 import net.minestom.server.data.DataContainer;
@@ -18,7 +20,6 @@ import net.minestom.server.utils.Direction;
 import net.minestom.server.utils.NBTUtils;
 import net.minestom.server.utils.clone.PublicCloneable;
 import net.minestom.server.utils.ownership.OwnershipHandler;
-import net.minestom.server.utils.validate.Check;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 import org.jglrxavpok.hephaistos.nbt.NBTCompound;
@@ -38,11 +39,11 @@ import java.util.*;
  */
 public class ItemStack implements DataContainer, PublicCloneable<ItemStack> {
 
-    public static final OwnershipHandler<Data> DATA_OWNERSHIP = new OwnershipHandler();
+    public static final OwnershipHandler<Data> DATA_OWNERSHIP = new OwnershipHandler<>();
     public static final String OWNERSHIP_DATA_KEY = "ownership_identifier";
     private static final StackingRule VANILLA_STACKING_RULE = new VanillaStackingRule(64);
 
-    private UUID identifier;
+    private final UUID identifier;
 
     private Material material;
 
@@ -56,7 +57,7 @@ public class ItemStack implements DataContainer, PublicCloneable<ItemStack> {
     private boolean unbreakable;
     private List<JsonMessage> lore;
 
-    private Map<Enchantment, Short> enchantmentMap;
+    private Object2ShortMap<Enchantment> enchantmentMap;
     private List<ItemAttribute> attributes;
 
     private int hideFlag;
@@ -78,7 +79,7 @@ public class ItemStack implements DataContainer, PublicCloneable<ItemStack> {
         this.damage = damage;
         this.lore = new ArrayList<>();
 
-        this.enchantmentMap = new HashMap<>();
+        this.enchantmentMap = new Object2ShortOpenHashMap<>();
         this.attributes = new ArrayList<>();
 
         this.itemMeta = findMeta();
@@ -117,7 +118,6 @@ public class ItemStack implements DataContainer, PublicCloneable<ItemStack> {
      * @throws NullPointerException if {@code defaultStackingRule} is null
      */
     public static void setDefaultStackingRule(@NotNull StackingRule defaultStackingRule) {
-        Check.notNull(defaultStackingRule, "StackingRule cannot be null!");
         ItemStack.defaultStackingRule = defaultStackingRule;
     }
 
@@ -341,7 +341,7 @@ public class ItemStack implements DataContainer, PublicCloneable<ItemStack> {
      * @param enchantment the enchantment type
      */
     public void removeEnchantment(@NotNull Enchantment enchantment) {
-        this.enchantmentMap.remove(enchantment);
+        this.enchantmentMap.removeShort(enchantment);
     }
 
     /**
@@ -581,7 +581,7 @@ public class ItemStack implements DataContainer, PublicCloneable<ItemStack> {
                 itemStack.setStackingRule(stackingRule);
             }
 
-            itemStack.enchantmentMap = new HashMap<>(enchantmentMap);
+            itemStack.enchantmentMap = new Object2ShortOpenHashMap<>(enchantmentMap);
             itemStack.attributes = new ArrayList<>(attributes);
 
             itemStack.hideFlag = hideFlag;
@@ -635,7 +635,6 @@ public class ItemStack implements DataContainer, PublicCloneable<ItemStack> {
      * @throws NullPointerException if {@code stackingRule} is null
      */
     public void setStackingRule(@NotNull StackingRule stackingRule) {
-        Check.notNull(stackingRule, "The stacking rule cannot be null!");
         this.stackingRule = stackingRule;
     }
 
diff --git a/src/main/java/net/minestom/server/item/firework/FireworkEffectType.java b/src/main/java/net/minestom/server/item/firework/FireworkEffectType.java
index 1762934ad..598764b7b 100644
--- a/src/main/java/net/minestom/server/item/firework/FireworkEffectType.java
+++ b/src/main/java/net/minestom/server/item/firework/FireworkEffectType.java
@@ -1,7 +1,7 @@
 package net.minestom.server.item.firework;
 
-import java.util.HashMap;
-import java.util.Map;
+import it.unimi.dsi.fastutil.bytes.Byte2ObjectMap;
+import it.unimi.dsi.fastutil.bytes.Byte2ObjectOpenHashMap;
 
 /**
  * An enumeration that representing all available firework types.
@@ -15,7 +15,7 @@ public enum FireworkEffectType {
     BURST((byte) 4),
     ;
 
-    private static final Map<Byte, FireworkEffectType> BY_ID = new HashMap<>();
+    private static final Byte2ObjectMap<FireworkEffectType> BY_ID = new Byte2ObjectOpenHashMap<>();
 
     static {
         for (FireworkEffectType value : values()) {
diff --git a/src/main/java/net/minestom/server/item/metadata/EnchantedBookMeta.java b/src/main/java/net/minestom/server/item/metadata/EnchantedBookMeta.java
index 69c60258e..7f280c8b2 100644
--- a/src/main/java/net/minestom/server/item/metadata/EnchantedBookMeta.java
+++ b/src/main/java/net/minestom/server/item/metadata/EnchantedBookMeta.java
@@ -1,17 +1,18 @@
 package net.minestom.server.item.metadata;
 
+import it.unimi.dsi.fastutil.objects.Object2ShortMap;
+import it.unimi.dsi.fastutil.objects.Object2ShortOpenHashMap;
 import net.minestom.server.item.Enchantment;
 import net.minestom.server.utils.NBTUtils;
 import org.jetbrains.annotations.NotNull;
 import org.jglrxavpok.hephaistos.nbt.NBTCompound;
 
 import java.util.Collections;
-import java.util.HashMap;
 import java.util.Map;
 
 public class EnchantedBookMeta extends ItemMeta {
 
-    private final Map<Enchantment, Short> storedEnchantmentMap = new HashMap<>();
+    private final Object2ShortMap<Enchantment> storedEnchantmentMap = new Object2ShortOpenHashMap<>();
 
     /**
      * Gets the stored enchantment map.
@@ -45,7 +46,7 @@ public class EnchantedBookMeta extends ItemMeta {
      * @param enchantment the enchantment type
      */
     public void removeStoredEnchantment(@NotNull Enchantment enchantment) {
-        this.storedEnchantmentMap.remove(enchantment);
+        this.storedEnchantmentMap.removeShort(enchantment);
     }
 
     /**
diff --git a/src/main/java/net/minestom/server/network/packet/server/play/CombatEventPacket.java b/src/main/java/net/minestom/server/network/packet/server/play/CombatEventPacket.java
index 685a2ad1c..86ddb4df5 100644
--- a/src/main/java/net/minestom/server/network/packet/server/play/CombatEventPacket.java
+++ b/src/main/java/net/minestom/server/network/packet/server/play/CombatEventPacket.java
@@ -31,19 +31,19 @@ public class CombatEventPacket implements ServerPacket {
         return packet;
     }
 
-    public static CombatEventPacket end(int durationInTicks, Optional<Entity> opponent) {
+    public static CombatEventPacket end(int durationInTicks, Entity opponent) {
         CombatEventPacket packet = new CombatEventPacket();
         packet.type = EventType.END_COMBAT;
         packet.duration = durationInTicks;
-        packet.opponent = opponent.map(Entity::getEntityId).orElse(-1);
+        packet.opponent = opponent != null ? opponent.getEntityId() : -1;
         return packet;
     }
 
-    public static CombatEventPacket death(Player player, Optional<Entity> killer, JsonMessage message) {
+    public static CombatEventPacket death(Player player, Entity killer, JsonMessage message) {
         CombatEventPacket packet = new CombatEventPacket();
         packet.type = EventType.DEATH;
         packet.playerID = player.getEntityId();
-        packet.opponent = killer.map(Entity::getEntityId).orElse(-1);
+        packet.opponent = killer != null ? killer.getEntityId() : -1;
         packet.deathMessage = message;
         return packet;
     }
diff --git a/src/main/java/net/minestom/server/registry/ResourceGatherer.java b/src/main/java/net/minestom/server/registry/ResourceGatherer.java
index c93165c0e..7af935d5b 100644
--- a/src/main/java/net/minestom/server/registry/ResourceGatherer.java
+++ b/src/main/java/net/minestom/server/registry/ResourceGatherer.java
@@ -4,6 +4,7 @@ import com.google.gson.Gson;
 import com.google.gson.JsonArray;
 import com.google.gson.JsonElement;
 import com.google.gson.JsonObject;
+import it.unimi.dsi.fastutil.io.FastBufferedInputStream;
 import org.apache.commons.codec.digest.DigestUtils;
 import org.apache.commons.lang3.StringUtils;
 import org.jetbrains.annotations.NotNull;
@@ -169,7 +170,7 @@ public class ResourceGatherer {
     private static File download(@NotNull String version, @NotNull String url, @NotNull String sha1Source) throws IOException {
         File target = new File(TMP_FOLDER, "server_" + version + ".jar");
         // Download
-        try (BufferedInputStream in = new BufferedInputStream(new URL(url).openStream())) {
+        try (FastBufferedInputStream in = new FastBufferedInputStream(new URL(url).openStream())) {
             Files.copy(in, target.toPath(), StandardCopyOption.REPLACE_EXISTING);
         } catch (IOException e) {
             throw new IOException("Failed to download Minecraft server jar.", e);
diff --git a/src/main/java/net/minestom/server/resourcepack/ResourcePack.java b/src/main/java/net/minestom/server/resourcepack/ResourcePack.java
index 18c2f3faf..f0837c540 100644
--- a/src/main/java/net/minestom/server/resourcepack/ResourcePack.java
+++ b/src/main/java/net/minestom/server/resourcepack/ResourcePack.java
@@ -14,7 +14,6 @@ public class ResourcePack {
     private final String hash;
 
     public ResourcePack(@NotNull String url, @Nullable String hash) {
-        Check.notNull(url, "The resource pack url cannot be null");
         this.url = url;
         // Optional, set to empty if null
         this.hash = hash == null ? "" : hash;
diff --git a/src/main/java/net/minestom/server/storage/StorageManager.java b/src/main/java/net/minestom/server/storage/StorageManager.java
index f5888a580..4e3bd718a 100644
--- a/src/main/java/net/minestom/server/storage/StorageManager.java
+++ b/src/main/java/net/minestom/server/storage/StorageManager.java
@@ -36,7 +36,6 @@ public final class StorageManager {
      * @return the specified {@link StorageLocation}
      */
     public StorageLocation getLocation(@NotNull String location, @NotNull StorageOptions storageOptions, @NotNull StorageSystem storageSystem) {
-        Check.notNull(storageOptions, "The storage option cannot be null");
         return locationMap.computeIfAbsent(location,
                 s -> new StorageLocation(storageSystem, location, storageOptions));
     }
diff --git a/src/main/java/net/minestom/server/utils/entity/EntityFinder.java b/src/main/java/net/minestom/server/utils/entity/EntityFinder.java
index e048ad979..2d8e34b44 100644
--- a/src/main/java/net/minestom/server/utils/entity/EntityFinder.java
+++ b/src/main/java/net/minestom/server/utils/entity/EntityFinder.java
@@ -281,20 +281,20 @@ public class EntityFinder {
                     closestDistance = distance;
                 }
             }
-            return Arrays.asList(entity);
+            return Collections.singletonList(entity);
         } else if (targetSelector == TargetSelector.RANDOM_PLAYER) {
             Collection<Player> instancePlayers = instance != null ?
                     instance.getPlayers() : MinecraftServer.getConnectionManager().getOnlinePlayers();
             final int index = ThreadLocalRandom.current().nextInt(instancePlayers.size());
             final Player player = instancePlayers.stream().skip(index).findFirst().orElseThrow();
-            return Arrays.asList(player);
+            return Collections.singletonList(player);
         } else if (targetSelector == TargetSelector.ALL_PLAYERS) {
             return new ArrayList<>(instance != null ?
                     instance.getPlayers() : MinecraftServer.getConnectionManager().getOnlinePlayers());
         } else if (targetSelector == TargetSelector.ALL_ENTITIES) {
             return new ArrayList<>(instance.getEntities());
         } else if (targetSelector == TargetSelector.SELF) {
-            return Arrays.asList(self);
+            return Collections.singletonList(self);
         }
         throw new IllegalStateException("Weird thing happened");
     }
diff --git a/src/main/java/net/minestom/server/world/DimensionType.java b/src/main/java/net/minestom/server/world/DimensionType.java
index 3906e4346..41293a67f 100644
--- a/src/main/java/net/minestom/server/world/DimensionType.java
+++ b/src/main/java/net/minestom/server/world/DimensionType.java
@@ -2,10 +2,10 @@ package net.minestom.server.world;
 
 import net.minestom.server.utils.NamespaceID;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 import org.jglrxavpok.hephaistos.nbt.NBTCompound;
 
 import java.util.Objects;
-import java.util.Optional;
 import java.util.concurrent.atomic.AtomicInteger;
 
 /**
@@ -24,7 +24,7 @@ public class DimensionType {
             .raidCapable(true)
             .skylightEnabled(true)
             .ceilingEnabled(false)
-            .fixedTime(Optional.empty())
+            .fixedTime(null)
             .ambientLight(0.0f)
             .logicalHeight(256)
             .infiniburn(NamespaceID.from("minecraft:infiniburn_overworld"))
@@ -39,7 +39,10 @@ public class DimensionType {
     private final float ambientLight;
     private final boolean ceilingEnabled;
     private final boolean skylightEnabled;
-    private final Optional<Long> fixedTime;
+
+    @Nullable
+    private final Long fixedTime;
+
     private final boolean raidCapable;
     private final boolean respawnAnchorSafe;
     private final boolean ultrawarm;
@@ -51,7 +54,7 @@ public class DimensionType {
     private final NamespaceID infiniburn;
 
     DimensionType(NamespaceID name, boolean natural, float ambientLight, boolean ceilingEnabled,
-                  boolean skylightEnabled, Optional<Long> fixedTime, boolean raidCapable,
+                  boolean skylightEnabled, @Nullable Long fixedTime, boolean raidCapable,
                   boolean respawnAnchorSafe, boolean ultrawarm, boolean bedSafe, String effects, boolean piglinSafe,
                   int logicalHeight, int coordinateScale, NamespaceID infiniburn) {
         this.name = name;
@@ -106,7 +109,7 @@ public class DimensionType {
                 .setInt("logical_height", logicalHeight)
                 .setInt("coordinate_scale", coordinateScale)
                 .setString("name", name.toString());
-        fixedTime.ifPresent(time -> nbt.setLong("fixed_time", time));
+        if (fixedTime != null) nbt.setLong("fixed_time", fixedTime);
         return nbt;
     }
 
@@ -143,7 +146,8 @@ public class DimensionType {
         return this.skylightEnabled;
     }
 
-    public Optional<Long> getFixedTime() {
+    @Nullable
+    public Long getFixedTime() {
         return this.fixedTime;
     }
 
@@ -203,7 +207,9 @@ public class DimensionType {
         private float ambientLight;
         private boolean ceilingEnabled;
         private boolean skylightEnabled;
-        private Optional<Long> fixedTime = Optional.empty();
+
+        @Nullable
+        private Long fixedTime = null;
         private boolean raidCapable;
         private boolean respawnAnchorSafe;
         private boolean ultrawarm;
@@ -242,7 +248,7 @@ public class DimensionType {
             return this;
         }
 
-        public DimensionType.DimensionTypeBuilder fixedTime(Optional<Long> fixedTime) {
+        public DimensionType.DimensionTypeBuilder fixedTime(Long fixedTime) {
             this.fixedTime = fixedTime;
             return this;
         }
diff --git a/src/test/java/demo/commands/DimensionCommand.java b/src/test/java/demo/commands/DimensionCommand.java
index bfbf0667b..285fba90f 100644
--- a/src/test/java/demo/commands/DimensionCommand.java
+++ b/src/test/java/demo/commands/DimensionCommand.java
@@ -36,8 +36,7 @@ public class DimensionCommand implements CommandProcessor {
         //    targetDimensionType = DimensionType.OVERWORLD;
         //}
 
-        DimensionType finalTargetDimensionType = targetDimensionType;
-        Optional<Instance> targetInstance = MinecraftServer.getInstanceManager().getInstances().stream().filter(in -> in.getDimensionType() == finalTargetDimensionType).findFirst();
+        Optional<Instance> targetInstance = MinecraftServer.getInstanceManager().getInstances().stream().filter(in -> in.getDimensionType() == targetDimensionType).findFirst();
         if (targetInstance.isPresent()) {
             player.sendMessage("You were in " + instance.getDimensionType());
             player.setInstance(targetInstance.get());
diff --git a/src/test/java/demo/commands/ReloadExtensionCommand.java b/src/test/java/demo/commands/ReloadExtensionCommand.java
index a7f21874b..305cba1bd 100644
--- a/src/test/java/demo/commands/ReloadExtensionCommand.java
+++ b/src/test/java/demo/commands/ReloadExtensionCommand.java
@@ -25,11 +25,10 @@ public class ReloadExtensionCommand extends Command {
     private static String[] extensionsName;
 
     static {
-        List<String> extensionsName = MinecraftServer.getExtensionManager().getExtensions()
+        ReloadExtensionCommand.extensionsName = MinecraftServer.getExtensionManager().getExtensions()
                 .stream()
                 .map(extension -> extension.getDescription().getName())
-                .collect(Collectors.toList());
-        ReloadExtensionCommand.extensionsName = extensionsName.toArray(new String[0]);
+                .toArray(String[]::new);
     }
 
     public ReloadExtensionCommand() {