diff --git a/plugin/src/main/java/me/filoghost/chestcommands/icon/BaseConfigurableIcon.java b/plugin/src/main/java/me/filoghost/chestcommands/icon/BaseConfigurableIcon.java
index 7c3ea8c..ba32909 100644
--- a/plugin/src/main/java/me/filoghost/chestcommands/icon/BaseConfigurableIcon.java
+++ b/plugin/src/main/java/me/filoghost/chestcommands/icon/BaseConfigurableIcon.java
@@ -233,7 +233,7 @@ public abstract class BaseConfigurableIcon implements Icon {
         cachedRendering = null;
     }
 
-    public String renderName(Player viewer) {
+    public @Nullable String renderName(Player viewer) {
         if (name == null) {
             return null;
         }
@@ -251,7 +251,7 @@ public abstract class BaseConfigurableIcon implements Icon {
         }
     }
 
-    public List<String> renderLore(Player viewer) {
+    public @Nullable List<String> renderLore(Player viewer) {
         if (lore == null) {
             return null;
         }
diff --git a/plugin/src/main/java/me/filoghost/chestcommands/icon/InternalConfigurableIcon.java b/plugin/src/main/java/me/filoghost/chestcommands/icon/InternalConfigurableIcon.java
index 557fde6..cba4206 100644
--- a/plugin/src/main/java/me/filoghost/chestcommands/icon/InternalConfigurableIcon.java
+++ b/plugin/src/main/java/me/filoghost/chestcommands/icon/InternalConfigurableIcon.java
@@ -23,6 +23,7 @@ import org.bukkit.entity.Player;
 import org.bukkit.inventory.ItemStack;
 import org.bukkit.inventory.meta.ItemMeta;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 import java.util.List;
 
@@ -166,7 +167,7 @@ public class InternalConfigurableIcon extends BaseConfigurableIcon implements Re
     }
 
     @Override
-    public ItemStack updateRendering(Player viewer, ItemStack currentRendering) {
+    public @Nullable ItemStack updateRendering(Player viewer, @Nullable ItemStack currentRendering) {
         if (currentRendering != null && shouldCacheRendering()) {
             // Internal icons do not change, no need to update if the item is already rendered
             return currentRendering;
diff --git a/plugin/src/main/java/me/filoghost/chestcommands/icon/RefreshableIcon.java b/plugin/src/main/java/me/filoghost/chestcommands/icon/RefreshableIcon.java
index 22d615a..6999f79 100644
--- a/plugin/src/main/java/me/filoghost/chestcommands/icon/RefreshableIcon.java
+++ b/plugin/src/main/java/me/filoghost/chestcommands/icon/RefreshableIcon.java
@@ -7,9 +7,10 @@ package me.filoghost.chestcommands.icon;
 
 import org.bukkit.entity.Player;
 import org.bukkit.inventory.ItemStack;
+import org.jetbrains.annotations.Nullable;
 
 public interface RefreshableIcon {
 
-    ItemStack updateRendering(Player viewer, ItemStack currentRendering);
+    @Nullable ItemStack updateRendering(Player viewer, @Nullable ItemStack currentRendering);
 
 }
diff --git a/plugin/src/main/java/me/filoghost/chestcommands/legacy/UpgradeList.java b/plugin/src/main/java/me/filoghost/chestcommands/legacy/UpgradeList.java
index 902be11..e325e92 100644
--- a/plugin/src/main/java/me/filoghost/chestcommands/legacy/UpgradeList.java
+++ b/plugin/src/main/java/me/filoghost/chestcommands/legacy/UpgradeList.java
@@ -20,6 +20,7 @@ import me.filoghost.fcommons.collection.CollectionUtils;
 import me.filoghost.fcommons.config.ConfigLoader;
 import me.filoghost.fcommons.config.exception.ConfigException;
 import me.filoghost.fcommons.logging.Log;
+import org.jetbrains.annotations.Nullable;
 
 import java.io.IOException;
 import java.nio.file.Path;
@@ -73,7 +74,7 @@ public class UpgradeList {
         }
     }
 
-    private static String readLegacyCommandSeparator(ConfigManager configManager) {
+    private static @Nullable String readLegacyCommandSeparator(ConfigManager configManager) {
         ConfigLoader settingsConfigLoader = configManager.getConfigLoader("config.yml");
 
         if (!settingsConfigLoader.fileExists()) {
diff --git a/plugin/src/main/java/me/filoghost/chestcommands/listener/CommandListener.java b/plugin/src/main/java/me/filoghost/chestcommands/listener/CommandListener.java
index f9aff65..cd3260a 100644
--- a/plugin/src/main/java/me/filoghost/chestcommands/listener/CommandListener.java
+++ b/plugin/src/main/java/me/filoghost/chestcommands/listener/CommandListener.java
@@ -11,6 +11,7 @@ import org.bukkit.event.EventHandler;
 import org.bukkit.event.EventPriority;
 import org.bukkit.event.Listener;
 import org.bukkit.event.player.PlayerCommandPreprocessEvent;
+import org.jetbrains.annotations.Nullable;
 
 public class CommandListener implements Listener {
 
@@ -30,7 +31,7 @@ public class CommandListener implements Listener {
         menu.openCheckingPermission(event.getPlayer());
     }
     
-    private static String getCommandName(String fullCommand) {
+    private static @Nullable String getCommandName(String fullCommand) {
         if (!fullCommand.startsWith("/")) {
             return null;
         }
diff --git a/plugin/src/main/java/me/filoghost/chestcommands/menu/MenuManager.java b/plugin/src/main/java/me/filoghost/chestcommands/menu/MenuManager.java
index 6c6d0bc..e21fb17 100644
--- a/plugin/src/main/java/me/filoghost/chestcommands/menu/MenuManager.java
+++ b/plugin/src/main/java/me/filoghost/chestcommands/menu/MenuManager.java
@@ -18,6 +18,7 @@ import org.bukkit.event.block.Action;
 import org.bukkit.inventory.Inventory;
 import org.bukkit.inventory.InventoryView;
 import org.bukkit.inventory.ItemStack;
+import org.jetbrains.annotations.Nullable;
 
 import java.util.Collection;
 import java.util.Collections;
@@ -95,7 +96,7 @@ public class MenuManager {
         }
     }
 
-    public static DefaultMenuView getOpenMenuView(Player player) {
+    public static @Nullable DefaultMenuView getOpenMenuView(Player player) {
         InventoryView inventoryView = player.getOpenInventory();
         if (inventoryView == null) {
             return null;
@@ -110,7 +111,7 @@ public class MenuManager {
     }
 
 
-    public static DefaultMenuView getOpenMenuView(Inventory inventory) {
+    public static @Nullable DefaultMenuView getOpenMenuView(Inventory inventory) {
         MenuInventoryHolder inventoryHolder = getMenuInventoryHolder(inventory);
         if (inventoryHolder != null) {
             return inventoryHolder.getMenuView();
@@ -119,7 +120,7 @@ public class MenuManager {
         }
     }
 
-    private static MenuInventoryHolder getMenuInventoryHolder(Inventory inventory) {
+    private static @Nullable MenuInventoryHolder getMenuInventoryHolder(Inventory inventory) {
         if (inventory.getHolder() instanceof MenuInventoryHolder) {
             return (MenuInventoryHolder) inventory.getHolder();
         } else {
diff --git a/plugin/src/main/java/me/filoghost/chestcommands/parsing/menu/ClickType.java b/plugin/src/main/java/me/filoghost/chestcommands/parsing/menu/ClickType.java
index 186b5eb..b33f8f0 100644
--- a/plugin/src/main/java/me/filoghost/chestcommands/parsing/menu/ClickType.java
+++ b/plugin/src/main/java/me/filoghost/chestcommands/parsing/menu/ClickType.java
@@ -6,6 +6,7 @@
 package me.filoghost.chestcommands.parsing.menu;
 
 import org.bukkit.event.block.Action;
+import org.jetbrains.annotations.Nullable;
 
 public enum ClickType {
 
@@ -13,7 +14,7 @@ public enum ClickType {
     RIGHT,
     BOTH;
 
-    public static ClickType fromOptions(boolean left, boolean right) {
+    public static @Nullable ClickType fromOptions(boolean left, boolean right) {
         if (left && right) {
             return BOTH;
         } else if (left) {
diff --git a/plugin/src/main/java/me/filoghost/chestcommands/placeholder/PlaceholderManager.java b/plugin/src/main/java/me/filoghost/chestcommands/placeholder/PlaceholderManager.java
index 06cbac4..c2cfcd2 100644
--- a/plugin/src/main/java/me/filoghost/chestcommands/placeholder/PlaceholderManager.java
+++ b/plugin/src/main/java/me/filoghost/chestcommands/placeholder/PlaceholderManager.java
@@ -5,8 +5,6 @@
  */
 package me.filoghost.chestcommands.placeholder;
 
-import java.util.ArrayList;
-import java.util.List;
 import me.filoghost.chestcommands.api.PlaceholderReplacer;
 import me.filoghost.chestcommands.hook.PlaceholderAPIHook;
 import me.filoghost.chestcommands.placeholder.scanner.PlaceholderMatch;
@@ -14,6 +12,10 @@ import me.filoghost.chestcommands.placeholder.scanner.PlaceholderScanner;
 import me.filoghost.fcommons.Preconditions;
 import org.bukkit.entity.Player;
 import org.bukkit.plugin.Plugin;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.ArrayList;
+import java.util.List;
 
 public class PlaceholderManager {
 
@@ -62,7 +64,7 @@ public class PlaceholderManager {
         return relativePlaceholderRegistry.getPlaceholderReplacer(placeholderMatch) != null;
     }
 
-    private static String getReplacement(PlaceholderMatch placeholderMatch, Player player) {
+    private static @Nullable String getReplacement(PlaceholderMatch placeholderMatch, Player player) {
         PlaceholderReplacer placeholderReplacer = relativePlaceholderRegistry.getPlaceholderReplacer(placeholderMatch);
 
         if (placeholderReplacer == null) {
diff --git a/plugin/src/main/java/me/filoghost/chestcommands/placeholder/PlaceholderRegistry.java b/plugin/src/main/java/me/filoghost/chestcommands/placeholder/PlaceholderRegistry.java
index a192586..3d20c61 100644
--- a/plugin/src/main/java/me/filoghost/chestcommands/placeholder/PlaceholderRegistry.java
+++ b/plugin/src/main/java/me/filoghost/chestcommands/placeholder/PlaceholderRegistry.java
@@ -5,12 +5,14 @@
  */
 package me.filoghost.chestcommands.placeholder;
 
-import java.util.HashMap;
-import java.util.LinkedHashMap;
-import java.util.Map;
 import me.filoghost.chestcommands.api.PlaceholderReplacer;
 import me.filoghost.chestcommands.placeholder.scanner.PlaceholderMatch;
 import org.bukkit.plugin.Plugin;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.HashMap;
+import java.util.LinkedHashMap;
+import java.util.Map;
 
 public class PlaceholderRegistry {
 
@@ -27,7 +29,7 @@ public class PlaceholderRegistry {
                 .put(plugin.getName(), placeholderReplacer);
     }
 
-    public PlaceholderReplacer getPlaceholderReplacer(PlaceholderMatch placeholderMatch) {
+    public @Nullable PlaceholderReplacer getPlaceholderReplacer(PlaceholderMatch placeholderMatch) {
         if (placeholderMatch.getPluginNamespace() == null) {
             PlaceholderReplacer internalReplacer = internalPlaceholders.get(placeholderMatch.getIdentifier());
             if (internalReplacer != null) {
diff --git a/plugin/src/main/java/me/filoghost/chestcommands/placeholder/PlaceholderString.java b/plugin/src/main/java/me/filoghost/chestcommands/placeholder/PlaceholderString.java
index 3a8e294..9f60328 100644
--- a/plugin/src/main/java/me/filoghost/chestcommands/placeholder/PlaceholderString.java
+++ b/plugin/src/main/java/me/filoghost/chestcommands/placeholder/PlaceholderString.java
@@ -6,6 +6,7 @@
 package me.filoghost.chestcommands.placeholder;
 
 import org.bukkit.entity.Player;
+import org.jetbrains.annotations.Nullable;
 
 public class PlaceholderString {
 
@@ -13,7 +14,7 @@ public class PlaceholderString {
     private final String stringWithStaticPlaceholders;
     private final boolean hasDynamicPlaceholders;
 
-    public static PlaceholderString of(String string) {
+    public static @Nullable PlaceholderString of(String string) {
         if (string != null) {
             return new PlaceholderString(string);
         } else {