diff --git a/src/main/java/io/github/thebusybiscuit/slimefun4/core/categories/MultiCategory.java b/src/main/java/io/github/thebusybiscuit/slimefun4/core/categories/MultiCategory.java
index 016a67bd3..3d9dca521 100644
--- a/src/main/java/io/github/thebusybiscuit/slimefun4/core/categories/MultiCategory.java
+++ b/src/main/java/io/github/thebusybiscuit/slimefun4/core/categories/MultiCategory.java
@@ -61,11 +61,13 @@ public class MultiCategory extends FlexCategory {
     }
 
     @Override
+    @ParametersAreNonnullByDefault
     public boolean isVisible(Player p, PlayerProfile profile, SlimefunGuideMode mode) {
         return true;
     }
 
     @Override
+    @ParametersAreNonnullByDefault
     public void open(Player p, PlayerProfile profile, SlimefunGuideMode mode) {
         openGuide(p, profile, mode, 1);
     }
diff --git a/src/main/java/io/github/thebusybiscuit/slimefun4/core/categories/SubCategory.java b/src/main/java/io/github/thebusybiscuit/slimefun4/core/categories/SubCategory.java
index e418e45ec..8da6cbafe 100644
--- a/src/main/java/io/github/thebusybiscuit/slimefun4/core/categories/SubCategory.java
+++ b/src/main/java/io/github/thebusybiscuit/slimefun4/core/categories/SubCategory.java
@@ -40,7 +40,7 @@ public class SubCategory extends Category {
     }
 
     @Override
-    public final boolean isHidden(Player p) {
+    public final boolean isHidden(@Nonnull Player p) {
         /*
          * Sub Categories are always hidden,
          * they won't show up in the normal guide view.
diff --git a/src/main/java/io/github/thebusybiscuit/slimefun4/implementation/guide/CheatSheetSlimefunGuide.java b/src/main/java/io/github/thebusybiscuit/slimefun4/implementation/guide/CheatSheetSlimefunGuide.java
index 4d5353d6a..f3594dcd8 100644
--- a/src/main/java/io/github/thebusybiscuit/slimefun4/implementation/guide/CheatSheetSlimefunGuide.java
+++ b/src/main/java/io/github/thebusybiscuit/slimefun4/implementation/guide/CheatSheetSlimefunGuide.java
@@ -1,6 +1,7 @@
 package io.github.thebusybiscuit.slimefun4.implementation.guide;
 
 import javax.annotation.Nonnull;
+import javax.annotation.ParametersAreNonnullByDefault;
 
 import java.util.LinkedList;
 import java.util.List;
@@ -73,6 +74,7 @@ public class CheatSheetSlimefunGuide extends SurvivalSlimefunGuide {
     }
 
     @Override
+    @ParametersAreNonnullByDefault
     public void createHeader(Player p, PlayerProfile profile, ChestMenu menu) {
         super.createHeader(p, profile, menu);