Cleanup

src/main/java/net/minestom/server/benchmark/BenchmarkManager.java

@@ -2,6 +2,7 @@ package net.minestom.server.benchmark;
 
 import net.minestom.server.MinecraftServer;
 import net.minestom.server.utils.time.UpdateOption;
+import net.minestom.server.utils.validate.Check;
 
 import java.lang.management.ManagementFactory;
 import java.lang.management.ThreadInfo;
@@ -37,8 +38,7 @@ public class BenchmarkManager {
     private long time;
 
     public void enable(UpdateOption updateOption) {
-        if (enabled)
+        Check.stateCondition(enabled, "A benchmark is already running, please disable it first.");
-            throw new IllegalStateException("A benchmark is already running, please disable it first.");
 
         this.updateOption = updateOption;
         time = updateOption.getTimeUnit().toMilliseconds(updateOption.getValue());

src/main/java/net/minestom/server/command/CommandManager.java

@@ -7,6 +7,7 @@ import net.minestom.server.entity.Player;
 import net.minestom.server.event.player.PlayerCommandEvent;
 import net.minestom.server.network.packet.server.play.DeclareCommandsPacket;
 import net.minestom.server.utils.ArrayUtils;
+import net.minestom.server.utils.validate.Check;
 
 import java.util.ArrayList;
 import java.util.HashMap;
@@ -29,10 +30,8 @@ public class CommandManager {
     }
 
     public boolean execute(Player source, String command) {
-        if (source == null)
+        Check.notNull(source, "Source cannot be null");
-            throw new NullPointerException("Source cannot be null");
+        Check.notNull(command, "Command string cannot be null");
-        if (command == null)
-            throw new NullPointerException("Command string cannot be null");
 
         PlayerCommandEvent playerCommandEvent = new PlayerCommandEvent(source, command);
         source.callEvent(PlayerCommandEvent.class, playerCommandEvent);

src/main/java/net/minestom/server/entity/Entity.java

@@ -22,6 +22,7 @@ import net.minestom.server.network.player.PlayerConnection;
 import net.minestom.server.utils.Vector;
 import net.minestom.server.utils.*;
 import net.minestom.server.utils.time.TimeUnit;
+import net.minestom.server.utils.validate.Check;
 
 import java.util.*;
 import java.util.concurrent.ConcurrentHashMap;
@@ -172,8 +173,7 @@ public abstract class Entity implements Viewable, EventHandler, DataContainer {
     }
 
     public void teleport(Position position, Runnable callback) {
-        if (instance == null)
+        Check.stateCondition(instance == null, "You need to use Entity#setInstance before teleporting an entity!");
-            throw new IllegalStateException("You need to use Entity#setInstance before teleporting an entity!");
 
         Runnable runnable = () -> {
             refreshPosition(position.getX(), position.getY(), position.getZ());
@@ -429,11 +429,9 @@ public abstract class Entity implements Viewable, EventHandler, DataContainer {
     }
 
     public void setInstance(Instance instance) {
-        if (instance == null)
+        Check.notNull(instance, "instance cannot be null!");
-            throw new IllegalArgumentException("instance cannot be null!");
+        Check.stateCondition(!MinecraftServer.getInstanceManager().getInstances().contains(instance),
-
+                "Instances need to be registered with InstanceManager#createInstanceContainer or InstanceManager#createSharedInstance");
-        if (!MinecraftServer.getInstanceManager().getInstances().contains(instance))
-            throw new IllegalStateException("Instances need to be registered with InstanceManager#createInstanceContainer or InstanceManager#createSharedInstance");
 
         if (this.instance != null) {
             this.instance.removeEntity(this);
@@ -472,8 +470,8 @@ public abstract class Entity implements Viewable, EventHandler, DataContainer {
     }
 
     public void addPassenger(Entity entity) {
-        if (instance == null)
+        Check.stateCondition(instance == null, "You need to set an instance using Entity#setInstance");
-            throw new IllegalStateException("You need to set an instance using Entity#setInstance");
+
         if (entity.getVehicle() != null) {
             entity.getVehicle().removePassenger(entity);
         }
@@ -485,8 +483,8 @@ public abstract class Entity implements Viewable, EventHandler, DataContainer {
     }
 
     public void removePassenger(Entity entity) {
-        if (instance == null)
+        Check.stateCondition(instance == null, "You need to set an instance using Entity#setInstance");
-            throw new IllegalStateException("You need to set an instance using Entity#setInstance");
+
         if (!passengers.contains(entity))
             return;
         this.passengers.remove(entity);

src/main/java/net/minestom/server/entity/EntityCreature.java

@@ -11,6 +11,7 @@ import net.minestom.server.utils.BlockPosition;
 import net.minestom.server.utils.ChunkUtils;
 import net.minestom.server.utils.Position;
 import net.minestom.server.utils.Vector;
+import net.minestom.server.utils.item.ItemStackUtils;
 import net.minestom.server.utils.time.TimeUnit;
 
 import java.util.LinkedList;
@@ -34,6 +35,14 @@ public abstract class EntityCreature extends LivingEntity {
 
     public EntityCreature(EntityType entityType, Position spawnPosition) {
         super(entityType.getId(), spawnPosition);
+
+        this.mainHandItem = ItemStack.getAirItem();
+        this.offHandItem = ItemStack.getAirItem();
+
+        this.helmet = ItemStack.getAirItem();
+        this.chestplate = ItemStack.getAirItem();
+        this.leggings = ItemStack.getAirItem();
+        this.boots = ItemStack.getAirItem();
     }
 
     @Override
@@ -150,7 +159,7 @@ public abstract class EntityCreature extends LivingEntity {
 
     @Override
     public void setItemInMainHand(ItemStack itemStack) {
-        this.mainHandItem = itemStack;
+        this.mainHandItem = ItemStackUtils.notNull(itemStack);
         syncEquipment(EntityEquipmentPacket.Slot.MAIN_HAND);
     }
 
@@ -161,7 +170,7 @@ public abstract class EntityCreature extends LivingEntity {
 
     @Override
     public void setItemInOffHand(ItemStack itemStack) {
-        this.offHandItem = itemStack;
+        this.offHandItem = ItemStackUtils.notNull(itemStack);
         syncEquipment(EntityEquipmentPacket.Slot.OFF_HAND);
     }
 
@@ -264,6 +273,8 @@ public abstract class EntityCreature extends LivingEntity {
     }
 
     private ItemStack getEquipmentItem(ItemStack itemStack, ArmorEquipEvent.ArmorSlot armorSlot) {
+        itemStack = ItemStackUtils.notNull(itemStack);
+
         ArmorEquipEvent armorEquipEvent = new ArmorEquipEvent(this, itemStack, armorSlot);
         callEvent(ArmorEquipEvent.class, armorEquipEvent);
         return armorEquipEvent.getArmorItem();

src/main/java/net/minestom/server/entity/EntityManager.java

@@ -6,6 +6,7 @@ import net.minestom.server.instance.Chunk;
 import net.minestom.server.instance.Instance;
 import net.minestom.server.instance.InstanceManager;
 import net.minestom.server.utils.thread.MinestomThread;
+import net.minestom.server.utils.validate.Check;
 
 import java.util.Set;
 import java.util.concurrent.ConcurrentLinkedQueue;
@@ -162,8 +163,8 @@ public class EntityManager {
                 PlayerLoginEvent loginEvent = new PlayerLoginEvent();
                 playerCache.callEvent(PlayerLoginEvent.class, loginEvent);
                 Instance spawningInstance = loginEvent.getSpawningInstance();
-                if (spawningInstance == null)
+
-                    throw new NullPointerException("You need to specify a spawning instance in the PlayerLoginEvent");
+                Check.notNull(spawningInstance, "You need to specify a spawning instance in the PlayerLoginEvent");
 
                 playerCache.setInstance(spawningInstance);
             });

src/main/java/net/minestom/server/entity/LivingEntity.java

@@ -272,8 +272,6 @@ public abstract class LivingEntity extends Entity implements EquipmentHandler {
 
     protected EntityEquipmentPacket getEquipmentPacket(EntityEquipmentPacket.Slot slot) {
         ItemStack itemStack = getEquipment(slot);
-        if (itemStack == null)
-            return null;
 
         EntityEquipmentPacket equipmentPacket = new EntityEquipmentPacket();
         equipmentPacket.entityId = getEntityId();

src/main/java/net/minestom/server/entity/Player.java

@@ -32,6 +32,7 @@ import net.minestom.server.sound.Sound;
 import net.minestom.server.sound.SoundCategory;
 import net.minestom.server.stat.PlayerStatistic;
 import net.minestom.server.utils.*;
+import net.minestom.server.utils.validate.Check;
 import net.minestom.server.world.Dimension;
 import net.minestom.server.world.LevelType;
 
@@ -159,7 +160,7 @@ public class Player extends LivingEntity {
         if (targetCustomBlock != null) {
             int animationCount = 10;
             long since = System.currentTimeMillis() - targetBlockTime;
-            byte stage = (byte) (since / (blockBreakTime / animationCount));
+            byte stage = (byte) (since / (blockBreakTime / animationCount) - 1);
             if (stage != targetLastStage) {
                 sendBlockBreakAnimation(targetBlockPosition, stage);
             }
@@ -374,10 +375,8 @@ public class Player extends LivingEntity {
 
     @Override
     public void setInstance(Instance instance) {
-        if (instance == null)
+        Check.notNull(instance, "instance cannot be null!");
-            throw new IllegalArgumentException("instance cannot be null!");
+        Check.argCondition(this.instance == instance, "Instance should be different than the current one");
-        if (this.instance == instance)
-            throw new IllegalArgumentException("Instance should be different than the current one");
 
         boolean firstSpawn = this.instance == null; // TODO: Handle player reconnections, must be false in that case too
         for (Chunk viewableChunk : viewableChunks) {
@@ -596,10 +595,16 @@ public class Player extends LivingEntity {
         sendUpdateHealthPacket();
     }
 
+    /**
+     * @return true if the player is currently eating, false otherwise
+     */
     public boolean isEating() {
         return isEating;
     }
 
+    /**
+     * @return the default eating time for the player
+     */
     public long getDefaultEatingTime() {
         return defaultEatingTime;
     }
@@ -690,8 +695,8 @@ public class Player extends LivingEntity {
     }
 
     public void setExp(float exp) {
-        if (!MathUtils.isBetween(exp, 0, 1))
+        Check.argCondition(!MathUtils.isBetween(exp, 0, 1), "Exp should be between 0 and 1");
-            throw new IllegalArgumentException("Exp should be between 0 and 1");
+
         this.exp = exp;
         sendExperienceUpdatePacket();
     }
@@ -811,10 +816,8 @@ public class Player extends LivingEntity {
 
     // Require sending chunk data after
     public void sendDimension(Dimension dimension) {
-        if (dimension == null)
+        Check.notNull(dimension, "Dimension cannot be null!");
-            throw new IllegalArgumentException("Dimension cannot be null!");
+        Check.argCondition(dimension.equals(getDimension()), "The dimension need to be different than the current one!");
-        if (dimension.equals(getDimension()))
-            throw new IllegalArgumentException("The dimension need to be different than the current one!");
 
         refreshDimension(dimension);
         RespawnPacket respawnPacket = new RespawnPacket();
@@ -847,15 +850,28 @@ public class Player extends LivingEntity {
         refreshGameMode(gameMode);
     }
 
+    /**
+     * Change the current held slot for the player
+     *
+     * @param slot the slot that the player has to held
+     * @throws IllegalArgumentException if {@code slot} is not between 0 and 8
+     */
     public void setHeldItemSlot(short slot) {
-        if (slot < 0 || slot > 8)
+        Check.argCondition(!MathUtils.isBetween(slot, 0, 8), "Slot has to be between 0 and 8");
-            throw new IllegalArgumentException("Slot has to be between 0 and 8");
+
         HeldItemChangePacket heldItemChangePacket = new HeldItemChangePacket();
         heldItemChangePacket.slot = slot;
         playerConnection.sendPacket(heldItemChangePacket);
         refreshHeldSlot(slot);
     }
 
+    /**
+     * @return the current held slot for the player
+     */
+    public short getHeldSlot() {
+        return heldSlot;
+    }
+
     public void setTeam(Team team) {
         if (this.team == team)
             return;
@@ -887,18 +903,25 @@ public class Player extends LivingEntity {
         }
     }
 
-    public short getHeldSlot() {
+    /**
-        return heldSlot;
+     * @return the currently open inventory, null if there is not (player inventory is not detected)
-    }
+     */
-
     public Inventory getOpenInventory() {
         return openInventory;
     }
 
+    /**
+     * Used to get the {@link CustomBlock} that the player is currently mining
+     *
+     * @return the currently mined {@link CustomBlock} by the player, null if there is not
+     */
     public CustomBlock getCustomBlockTarget() {
         return targetCustomBlock;
     }
 
+    /**
+     * @return an unmodifiable {@link Set} containing all the current player viewable boss bars
+     */
     public Set<BossBar> getBossBars() {
         return Collections.unmodifiableSet(bossBars);
     }
@@ -910,8 +933,7 @@ public class Player extends LivingEntity {
      * @return true if the inventory has been opened/sent to the player, false otherwise (cancelled by event)
      */
     public boolean openInventory(Inventory inventory) {
-        if (inventory == null)
+        Check.notNull(inventory, "Inventory cannot be null, use Player#closeInventory() to close current");
-            throw new IllegalArgumentException("Inventory cannot be null, use Player#closeInventory() to close current");
 
         InventoryOpenEvent inventoryOpenEvent = new InventoryOpenEvent(this, inventory);
 
@@ -970,10 +992,16 @@ public class Player extends LivingEntity {
         inventory.update();
     }
 
+    /**
+     * @return an unmodifiable {@link Set} containing all the chunks that the player sees
+     */
     public Set<Chunk> getViewableChunks() {
         return Collections.unmodifiableSet(viewableChunks);
     }
 
+    /**
+     * Remove all the boss bars that the player has
+     */
     public void clearBossBars() {
         this.bossBars.forEach(bossBar -> bossBar.removeViewer(this));
     }
@@ -996,8 +1024,7 @@ public class Player extends LivingEntity {
     }
 
     public void setPermissionLevel(int permissionLevel) {
-        if (!MathUtils.isBetween(permissionLevel, 0, 4))
+        Check.argCondition(!MathUtils.isBetween(permissionLevel, 0, 4), "permissionLevel has to be between 0 and 4");
-            throw new IllegalArgumentException("permissionLevel has to be between 0 and 4");
 
         this.permissionLevel = permissionLevel;
 

src/main/java/net/minestom/server/event/inventory/InventoryClickEvent.java

@@ -24,7 +24,7 @@ public class InventoryClickEvent extends Event {
     /**
      * Can be null if the clicked inventory is the player one
      *
-     * @return
+     * @return the inventory where the click happened, null if this is the player's inventory
      */
     public Inventory getInventory() {
         return inventory;

src/main/java/net/minestom/server/event/inventory/InventoryOpenEvent.java

@@ -3,6 +3,7 @@ package net.minestom.server.event.inventory;
 import net.minestom.server.entity.Player;
 import net.minestom.server.event.CancellableEvent;
 import net.minestom.server.inventory.Inventory;
+import net.minestom.server.utils.validate.Check;
 
 public class InventoryOpenEvent extends CancellableEvent {
 
@@ -23,9 +24,7 @@ public class InventoryOpenEvent extends CancellableEvent {
     }
 
     public void setInventory(Inventory inventory) {
-        if (inventory == null)
+        Check.notNull(inventory, "Inventory cannot be null!");
-            throw new NullPointerException("Inventory cannot be null!");
-
         this.inventory = inventory;
     }
 }

src/main/java/net/minestom/server/event/inventory/InventoryPreClickEvent.java

@@ -4,6 +4,7 @@ import net.minestom.server.event.CancellableEvent;
 import net.minestom.server.inventory.Inventory;
 import net.minestom.server.inventory.click.ClickType;
 import net.minestom.server.item.ItemStack;
+import net.minestom.server.utils.item.ItemStackUtils;
 
 public class InventoryPreClickEvent extends CancellableEvent {
 
@@ -24,7 +25,7 @@ public class InventoryPreClickEvent extends CancellableEvent {
     /**
      * Can be null if the clicked inventory is the player one
      *
-     * @return
+     * @return the inventory where the click happened, null if this is the player's inventory
      */
     public Inventory getInventory() {
         return inventory;
@@ -43,7 +44,7 @@ public class InventoryPreClickEvent extends CancellableEvent {
     }
 
     public void setClickedItem(ItemStack clickedItem) {
-        this.clickedItem = clickedItem;
+        this.clickedItem = ItemStackUtils.notNull(clickedItem);
     }
 
     public ItemStack getCursorItem() {
@@ -51,6 +52,6 @@ public class InventoryPreClickEvent extends CancellableEvent {
     }
 
     public void setCursorItem(ItemStack cursorItem) {
-        this.cursorItem = cursorItem;
+        this.cursorItem = ItemStackUtils.notNull(cursorItem);
     }
 }

src/main/java/net/minestom/server/event/item/ArmorEquipEvent.java

@@ -3,7 +3,7 @@ package net.minestom.server.event.item;
 import net.minestom.server.entity.LivingEntity;
 import net.minestom.server.event.Event;
 import net.minestom.server.item.ItemStack;
-import net.minestom.server.network.packet.server.play.EntityEquipmentPacket;
+import net.minestom.server.utils.item.ItemStackUtils;
 
 public class ArmorEquipEvent extends Event {
 
@@ -26,7 +26,7 @@ public class ArmorEquipEvent extends Event {
     }
 
     public void setArmorItem(ItemStack armorItem) {
-        this.armorItem = armorItem;
+        this.armorItem = ItemStackUtils.notNull(armorItem);
     }
 
     public ArmorSlot getArmorSlot() {
@@ -37,21 +37,6 @@ public class ArmorEquipEvent extends Event {
         HELMET,
         CHESTPLATE,
         LEGGINGS,
-        BOOTS;
+        BOOTS
-
-        public EntityEquipmentPacket.Slot toEquipmentPacketSlot() {
-            switch (this) {
-                case HELMET:
-                    return EntityEquipmentPacket.Slot.HELMET;
-                case CHESTPLATE:
-                    return EntityEquipmentPacket.Slot.CHESTPLATE;
-                case LEGGINGS:
-                    return EntityEquipmentPacket.Slot.LEGGINGS;
-                case BOOTS:
-                    return EntityEquipmentPacket.Slot.BOOTS;
-                default:
-                    return null;
-            }
-        }
     }
 }

src/main/java/net/minestom/server/instance/Chunk.java

@@ -20,6 +20,7 @@ import net.minestom.server.utils.PacketUtils;
 import net.minestom.server.utils.SerializerUtils;
 import net.minestom.server.utils.time.CooldownUtils;
 import net.minestom.server.utils.time.UpdateOption;
+import net.minestom.server.utils.validate.Check;
 
 import java.io.ByteArrayOutputStream;
 import java.io.DataOutputStream;
@@ -78,8 +79,7 @@ public class Chunk implements Viewable {
 
     public void UNSAFE_setCustomBlock(int x, int y, int z, short visualBlockId, short customBlockId, Data data) {
         CustomBlock customBlock = BLOCK_MANAGER.getCustomBlock(customBlockId);
-        if (customBlock == null)
+        Check.notNull(customBlock, "The custom block " + customBlockId + " does not exist or isn't registered");
-            throw new IllegalArgumentException("The custom block " + customBlockId + " does not exist or isn't registered");
 
         UNSAFE_setCustomBlock(x, y, z, visualBlockId, customBlock, data);
     }

src/main/java/net/minestom/server/instance/InstanceManager.java

@@ -3,6 +3,7 @@ package net.minestom.server.instance;
 import net.minestom.server.MinecraftServer;
 import net.minestom.server.storage.StorageFolder;
 import net.minestom.server.utils.thread.MinestomThread;
+import net.minestom.server.utils.validate.Check;
 import net.minestom.server.world.Dimension;
 
 import java.util.Collections;
@@ -42,8 +43,7 @@ public class InstanceManager {
 
     public SharedInstance createSharedInstance(SharedInstance sharedInstance) {
         InstanceContainer instanceContainer = sharedInstance.getInstanceContainer();
-        if (instanceContainer == null)
+        Check.notNull(instanceContainer, "SharedInstance needs to have an InstanceContainer to be created!");
-            throw new NullPointerException("SharedInstance needs to have an InstanceContainer to be created!");
 
         instanceContainer.addSharedInstance(sharedInstance);
         this.instances.add(sharedInstance);
@@ -51,8 +51,7 @@ public class InstanceManager {
     }
 
     public SharedInstance createSharedInstance(InstanceContainer instanceContainer) {
-        if (instanceContainer == null)
+        Check.notNull(instanceContainer, "Instance container cannot be null when creating a SharedInstance!");
-            throw new IllegalArgumentException("Instance container cannot be null when creating a SharedInstance!");
 
         SharedInstance sharedInstance = new SharedInstance(UUID.randomUUID(), instanceContainer);
         return createSharedInstance(sharedInstance);

src/main/java/net/minestom/server/inventory/EquipmentHandler.java

@@ -70,7 +70,7 @@ public interface EquipmentHandler {
             case BOOTS:
                 return getBoots();
             default:
-                throw new NullPointerException("Equipment slot cannot be null");
+                return null;
         }
     }
 

src/main/java/net/minestom/server/inventory/Inventory.java

@@ -11,7 +11,10 @@ import net.minestom.server.item.ItemStack;
 import net.minestom.server.network.packet.server.play.SetSlotPacket;
 import net.minestom.server.network.packet.server.play.WindowItemsPacket;
 import net.minestom.server.network.packet.server.play.WindowPropertyPacket;
+import net.minestom.server.utils.MathUtils;
 import net.minestom.server.utils.inventory.PlayerInventoryUtils;
+import net.minestom.server.utils.item.ItemStackUtils;
+import net.minestom.server.utils.validate.Check;
 
 import java.util.Arrays;
 import java.util.Collections;
@@ -77,8 +80,8 @@ public class Inventory implements InventoryModifier, InventoryClickHandler, View
 
     @Override
     public void setItemStack(int slot, ItemStack itemStack) {
-        if (slot < 0 || slot > getSize())
+        Check.argCondition(!MathUtils.isBetween(slot, 0, getSize()),
-            throw new IllegalArgumentException(inventoryType.toString() + " does not have slot " + slot);
+                inventoryType.toString() + " does not have slot " + slot);
 
         safeItemInsert(slot, itemStack);
     }
@@ -160,7 +163,7 @@ public class Inventory implements InventoryModifier, InventoryClickHandler, View
 
     private void safeItemInsert(int slot, ItemStack itemStack) {
         synchronized (this) {
-            itemStack = itemStack == null ? ItemStack.getAirItem() : itemStack;
+            itemStack = ItemStackUtils.notNull(itemStack);
             this.itemStacks[slot] = itemStack;
             SetSlotPacket setSlotPacket = new SetSlotPacket();
             setSlotPacket.windowId = getWindowId();

src/main/java/net/minestom/server/inventory/PlayerInventory.java

@@ -14,6 +14,7 @@ import net.minestom.server.network.packet.server.play.SetSlotPacket;
 import net.minestom.server.network.packet.server.play.WindowItemsPacket;
 import net.minestom.server.network.player.PlayerConnection;
 import net.minestom.server.utils.MathUtils;
+import net.minestom.server.utils.item.ItemStackUtils;
 
 import java.util.Arrays;
 import java.util.List;
@@ -181,12 +182,12 @@ public class PlayerInventory implements InventoryModifier, InventoryClickHandler
     }
 
     public void setCursorItem(ItemStack cursorItem) {
-        this.cursorItem = cursorItem;
+        this.cursorItem = ItemStackUtils.notNull(cursorItem);
     }
 
     private void safeItemInsert(int slot, ItemStack itemStack) {
         synchronized (this) {
-            itemStack = itemStack == null ? ItemStack.getAirItem() : itemStack;
+            itemStack = ItemStackUtils.notNull(itemStack);
 
             EntityEquipmentPacket.Slot equipmentSlot;
 
@@ -208,7 +209,8 @@ public class PlayerInventory implements InventoryModifier, InventoryClickHandler
                 }
 
                 if (armorEquipEvent != null) {
-                    equipmentSlot = armorEquipEvent.getArmorSlot().toEquipmentPacketSlot();
+                    ArmorEquipEvent.ArmorSlot armorSlot = armorEquipEvent.getArmorSlot();
+                    equipmentSlot = EntityEquipmentPacket.Slot.fromArmorSlot(armorSlot);
                     player.callEvent(ArmorEquipEvent.class, armorEquipEvent);
                     itemStack = armorEquipEvent.getArmorItem();
                 } else {
@@ -216,13 +218,11 @@ public class PlayerInventory implements InventoryModifier, InventoryClickHandler
                 }
             }
 
-            if (itemStack != null) {
+            this.items[slot] = itemStack;
-                this.items[slot] = itemStack;
-            }
 
             // Refresh slot
-            refreshSlot(slot);
+            update();
-            //update(); in case of problems
+            //refreshSlot(slot); seems to break things concerning +64 stacks
 
             // Sync equipment
             if (equipmentSlot != null) {

src/main/java/net/minestom/server/item/ItemStack.java

@@ -3,6 +3,7 @@ package net.minestom.server.item;
 import net.minestom.server.data.Data;
 import net.minestom.server.data.DataContainer;
 import net.minestom.server.item.rule.VanillaStackingRule;
+import net.minestom.server.utils.validate.Check;
 
 import java.util.*;
 
@@ -208,11 +209,9 @@ public class ItemStack implements DataContainer {
         return stackingRule;
     }
 
-    public void setStackingRule(StackingRule stackingRule) {
+    public static void setDefaultStackingRule(StackingRule defaultStackingRule) {
-        if (stackingRule == null)
+        Check.notNull(defaultStackingRule, "StackingRule cannot be null!");
-            throw new NullPointerException("StackingRule cannot be null!");
+        ItemStack.defaultStackingRule = defaultStackingRule;
-
-        this.stackingRule = stackingRule;
     }
 
     @Override
@@ -229,11 +228,9 @@ public class ItemStack implements DataContainer {
         return defaultStackingRule;
     }
 
-    public static void setDefaultStackingRule(StackingRule defaultStackingRule) {
+    public void setStackingRule(StackingRule stackingRule) {
-        if (defaultStackingRule == null)
+        Check.notNull(stackingRule, "StackingRule cannot be null!");
-            throw new NullPointerException("StackingRule cannot be null!");
+        this.stackingRule = stackingRule;
-
-        ItemStack.defaultStackingRule = defaultStackingRule;
     }
 
     private byte getBitModifier(ItemFlag hideFlag) {

src/main/java/net/minestom/server/listener/ChatMessageListener.java

@@ -12,6 +12,7 @@ import net.minestom.server.entity.Player;
 import net.minestom.server.event.player.PlayerChatEvent;
 import net.minestom.server.event.player.PlayerCommandEvent;
 import net.minestom.server.network.packet.client.play.ClientChatMessagePacket;
+import net.minestom.server.utils.validate.Check;
 
 import java.util.function.Function;
 
@@ -55,8 +56,7 @@ public class ChatMessageListener {
         player.callCancellableEvent(PlayerChatEvent.class, playerChatEvent, () -> {
 
             Function<PlayerChatEvent, TextComponent> formatFunction = playerChatEvent.getChatFormatFunction();
-            if (formatFunction == null)
+            Check.notNull(formatFunction, "PlayerChatEvent#getChatFormatFunction cannot be null!");
-                throw new NullPointerException("PlayerChatEvent#chatFormat cannot be null!");
 
             TextComponent textObject = formatFunction.apply(playerChatEvent);
 

src/main/java/net/minestom/server/network/packet/server/play/DeclareRecipesPacket.java

@@ -4,6 +4,7 @@ import net.minestom.server.item.ItemStack;
 import net.minestom.server.network.packet.PacketWriter;
 import net.minestom.server.network.packet.server.ServerPacket;
 import net.minestom.server.network.packet.server.ServerPacketIdentifier;
+import net.minestom.server.utils.validate.Check;
 
 public class DeclareRecipesPacket implements ServerPacket {
 
@@ -11,8 +12,8 @@ public class DeclareRecipesPacket implements ServerPacket {
 
     @Override
     public void write(PacketWriter writer) {
-        if (recipes == null)
+        Check.notNull(recipes, "Recipes cannot be null!");
-            throw new NullPointerException("Recipes cannot be null!");
+
         writer.writeVarInt(recipes.length);
         for (Recipe recipe : recipes) {
             recipe.write(writer);

src/main/java/net/minestom/server/network/packet/server/play/EntityEquipmentPacket.java

@@ -1,5 +1,6 @@
 package net.minestom.server.network.packet.server.play;
 
+import net.minestom.server.event.item.ArmorEquipEvent;
 import net.minestom.server.item.ItemStack;
 import net.minestom.server.network.packet.PacketWriter;
 import net.minestom.server.network.packet.server.ServerPacket;
@@ -29,7 +30,23 @@ public class EntityEquipmentPacket implements ServerPacket {
         BOOTS,
         LEGGINGS,
         CHESTPLATE,
-        HELMET
+        HELMET;
+
+        public static Slot fromArmorSlot(ArmorEquipEvent.ArmorSlot armorSlot) {
+            switch (armorSlot) {
+                case HELMET:
+                    return HELMET;
+                case CHESTPLATE:
+                    return CHESTPLATE;
+                case LEGGINGS:
+                    return LEGGINGS;
+                case BOOTS:
+                    return BOOTS;
+                default:
+                    return null;
+            }
+        }
+
     }
 
 }

src/main/java/net/minestom/server/scoreboard/Sidebar.java

@@ -7,6 +7,7 @@ import net.minestom.server.network.packet.server.play.DisplayScoreboardPacket;
 import net.minestom.server.network.packet.server.play.ScoreboardObjectivePacket;
 import net.minestom.server.network.packet.server.play.UpdateScorePacket;
 import net.minestom.server.network.player.PlayerConnection;
+import net.minestom.server.utils.validate.Check;
 
 import java.util.Iterator;
 import java.util.LinkedList;
@@ -60,15 +61,13 @@ public class Sidebar implements Viewable {
 
     public void createLine(ScoreboardLine scoreboardLine) {
         synchronized (lines) {
-            if (lines.size() >= MAX_LINES_COUNT)
+            Check.stateCondition(lines.size() >= MAX_LINES_COUNT, "You cannot have more than " + MAX_LINES_COUNT + "  lines");
-                throw new IllegalStateException("You cannot have more than " + MAX_LINES_COUNT + "  lines");
+            Check.argCondition(lines.contains(scoreboardLine), "You cannot add two times the same ScoreboardLine");
-            if (lines.contains(scoreboardLine))
-                throw new IllegalArgumentException("You cannot add two times the same ScoreboardLine");
 
             // Check ID duplication
             for (ScoreboardLine line : lines) {
-                if (line.id.equals(scoreboardLine.id))
+                Check.argCondition(line.id.equals(scoreboardLine.id),
-                    throw new IllegalArgumentException("You cannot add two ScoreboardLine with the same id");
+                        "You cannot add two ScoreboardLine with the same id");
             }
 
             // Setup line

src/main/java/net/minestom/server/storage/StorageFolder.java

@@ -9,6 +9,7 @@ import net.minestom.server.data.SerializableData;
 import net.minestom.server.network.packet.PacketReader;
 import net.minestom.server.network.packet.PacketWriter;
 import net.minestom.server.reader.DataReader;
+import net.minestom.server.utils.validate.Check;
 
 import java.io.IOException;
 import java.util.HashMap;
@@ -50,8 +51,7 @@ public class StorageFolder {
 
     public <T> void set(String key, T object, Class<T> type) {
         DataType<T> dataType = DATA_MANAGER.getDataType(type);
-        if (dataType == null)
+        Check.notNull(dataType, "You can only save registered DataType type!");
-            throw new NullPointerException("You can only save registered DataType type!");
 
         PacketWriter packetWriter = new PacketWriter();
         dataType.encode(packetWriter, object); // Encode
@@ -62,8 +62,7 @@ public class StorageFolder {
 
     public <T> T get(String key, Class<T> type) {
         DataType<T> dataType = DATA_MANAGER.getDataType(type);
-        if (dataType == null)
+        Check.notNull(dataType, "You can only save registered DataType type!");
-            throw new NullPointerException("You can only save registered DataType type!");
 
         byte[] data = get(key);
         if (data == null)

src/main/java/net/minestom/server/storage/StorageManager.java

@@ -1,5 +1,6 @@
 package net.minestom.server.storage;
 
+import net.minestom.server.utils.validate.Check;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -41,8 +42,8 @@ public class StorageManager {
      * @throws NullPointerException if no default StorageSystem is defined {@link #defineDefaultStorageSystem(Supplier)}
      */
     public StorageFolder getFolder(String folderPath) {
-        if (defaultStorageSystemSupplier == null)
+        Check.notNull(defaultStorageSystemSupplier,
-            throw new NullPointerException("You need to either define a default storage system or specify your storage system for this specific folder");
+                "You need to either define a default storage system or specify your storage system for this specific folder");
 
         StorageSystem storageSystem = defaultStorageSystemSupplier.get();
         return getFolder(folderPath, storageSystem);

src/main/java/net/minestom/server/utils/consumer/StringConsumer.java

@@ -1,7 +0,0 @@
-package net.minestom.server.utils.consumer;
-
-public interface StringConsumer {
-
-    void accept(String string, int length);
-
-}

src/main/java/net/minestom/server/utils/inventory/PlayerInventoryUtils.java

@@ -21,6 +21,7 @@ public class PlayerInventoryUtils {
      *
      * @param slot   the packet slot
      * @param offset the slot count separating the up part of the inventory to the bottom part (armor/craft in PlayerInventory, inventory slots in others)
+     *               the offset for the player inventory is {@link #OFFSET}
      * @return a packet which can be use internally with Minestom
      */
     public static int convertSlot(int slot, int offset) {

src/main/java/net/minestom/server/utils/item/ItemStackUtils.java

@@ -0,0 +1,15 @@
+package net.minestom.server.utils.item;
+
+import net.minestom.server.item.ItemStack;
+
+public class ItemStackUtils {
+
+    /**
+     * @param itemStack the ItemStack to return if not null
+     * @return {@code itemStack} if not null, {@link ItemStack#getAirItem()} otherwise
+     */
+    public static ItemStack notNull(ItemStack itemStack) {
+        return itemStack == null ? ItemStack.getAirItem() : itemStack;
+    }
+
+}

src/main/java/net/minestom/server/utils/validate/Check.java

@@ -0,0 +1,22 @@
+package net.minestom.server.utils.validate;
+
+import java.util.Objects;
+
+public class Check {
+
+    public static void notNull(Object object, String reason) {
+        if (Objects.isNull(object))
+            throw new NullPointerException(reason);
+    }
+
+    public static void argCondition(boolean condition, String reason) {
+        if (condition)
+            throw new IllegalArgumentException(reason);
+    }
+
+    public static void stateCondition(boolean condition, String reason) {
+        if (condition)
+            throw new IllegalStateException(reason);
+    }
+
+}