Fix "/is admin level" page 3+ in 1.12-, also remove gaps

src/main/java/me/goodandevil/skyblock/command/commands/ValueCommand.java

@@ -56,7 +56,7 @@ public class ValueCommand extends SubCommand {
 					materials = Materials.fromString(player.getItemInHand().getType().name());
 				}
 
-				if (materials != null && levellingManager.containsMaterials(materials)) {
+				if (materials != null && levellingManager.containsMaterial(materials)) {
 					Material material = levellingManager.getMaterial(materials);
 					double level = (double) material.getPoints()
 							/ (double) fileManager.getConfig(new File(skyblock.getDataFolder(), "config.yml"))

src/main/java/me/goodandevil/skyblock/levelling/LevellingManager.java

@@ -1,5 +1,23 @@
 package me.goodandevil.skyblock.levelling;
 
+import java.io.File;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.logging.Level;
+
+import org.bukkit.Bukkit;
+import org.bukkit.ChunkSnapshot;
+import org.bukkit.Location;
+import org.bukkit.World;
+import org.bukkit.configuration.file.FileConfiguration;
+import org.bukkit.entity.Player;
+import org.bukkit.inventory.ItemStack;
+import org.bukkit.scheduler.BukkitRunnable;
+
 import me.goodandevil.skyblock.SkyBlock;
 import me.goodandevil.skyblock.api.event.island.IslandLevelChangeEvent;
 import me.goodandevil.skyblock.config.FileManager.Config;
@@ -12,23 +30,6 @@ import me.goodandevil.skyblock.utils.version.Materials;
 import me.goodandevil.skyblock.utils.version.NMSUtil;
 import me.goodandevil.skyblock.utils.version.Sounds;
 import me.goodandevil.skyblock.world.WorldManager;
-import org.bukkit.Bukkit;
-import org.bukkit.ChunkSnapshot;
-import org.bukkit.Location;
-import org.bukkit.World;
-import org.bukkit.configuration.file.FileConfiguration;
-import org.bukkit.entity.Player;
-import org.bukkit.inventory.ItemStack;
-import org.bukkit.scheduler.BukkitRunnable;
-
-import java.io.File;
-import java.lang.reflect.InvocationTargetException;
-import java.lang.reflect.Method;
-import java.util.ArrayList;
-import java.util.HashMap;
-import java.util.List;
-import java.util.Map;
-import java.util.logging.Level;
 
 public class LevellingManager {
 
@@ -196,15 +197,15 @@ public class LevellingManager {
         FileConfiguration configLoad = config.getFileConfiguration();
         
         if (configLoad.getString("Materials") != null) {
-            for (String materialList : configLoad.getConfigurationSection("Materials").getKeys(false)) {
+            for (String materialKey : configLoad.getConfigurationSection("Materials").getKeys(false)) {
                 try {
-                    Materials materials = Materials.fromString(materialList);
+                    Materials material = Materials.fromString(materialKey);
                     
-                    if (!containsMaterials(materials)) {
+                    if (!containsMaterial(material)) {
-                        addMaterial(materials, configLoad.getInt("Materials." + materialList + ".Points"));
+                        addMaterial(material, configLoad.getInt("Materials." + materialKey + ".Points"));
                     }
                 } catch (Exception e) {
-                    Bukkit.getServer().getLogger().log(Level.WARNING, "SkyBlock | Error: The material '" + materialList
+                    Bukkit.getServer().getLogger().log(Level.WARNING, "SkyBlock | Error: The material '" + materialKey
                             + "' is not a Material type. Make sure the material name is a 1.13 material name. Please correct this in the 'levelling.yml' file.");
                 }
             }
@@ -223,7 +224,7 @@ public class LevellingManager {
         materialStorage.remove(material);
     }
 
-    public boolean containsMaterials(Materials materials) {
+    public boolean containsMaterial(Materials materials) {
         for (Material materialList : materialStorage) {
             if (materialList.getMaterials().name().equals(materials.name())) {
                 return true;

src/main/java/me/goodandevil/skyblock/menus/admin/Levelling.java

@@ -3,6 +3,7 @@ package me.goodandevil.skyblock.menus.admin;
 import java.io.File;
 import java.io.IOException;
 import java.util.List;
+import java.util.stream.Collectors;
 
 import org.bukkit.Bukkit;
 import org.bukkit.ChatColor;
@@ -13,6 +14,7 @@ import org.bukkit.event.EventHandler;
 import org.bukkit.event.Listener;
 import org.bukkit.event.inventory.ClickType;
 import org.bukkit.event.inventory.InventoryClickEvent;
+import org.bukkit.inventory.Inventory;
 import org.bukkit.inventory.ItemStack;
 import org.bukkit.inventory.meta.ItemMeta;
 
@@ -56,6 +58,16 @@ public class Levelling implements Listener {
 
 		List<me.goodandevil.skyblock.levelling.Material> levellingMaterials = levellingManager.getMaterials();
 		
+		// Filter out materials that won't be displayed in the GUI properly
+        Inventory testInventory = Bukkit.createInventory(null, 9);
+        levellingMaterials = levellingMaterials.stream().filter(x -> {
+            ItemStack itemStack = new ItemStack(MaterialUtil.correctMaterial(x.getItemStack().getType()), 1, x.getItemStack().getDurability());
+            if (itemStack == null || itemStack.getItemMeta() == null) return false;
+            testInventory.clear();
+            testInventory.setItem(0, itemStack);
+            return testInventory.getItem(0) != null;
+        }).collect(Collectors.toList());
+
 		Config config = fileManager.getConfig(new File(skyblock.getDataFolder(), "language.yml"));
 		FileConfiguration configLoad = config.getFileConfiguration();
 
@@ -315,7 +327,7 @@ public class Levelling implements Listener {
 											messageManager.sendMessage(player,
 													configLoad.getString("Island.Admin.Levelling.Permission.Message"));
 											soundManager.playSound(player, Sounds.ANVIL_LAND.bukkitSound(), 1.0F, 1.0F);
-										} else if (levellingManager.containsMaterials(materials)) {
+										} else if (levellingManager.containsMaterial(materials)) {
 											if (event1.getName().matches("[0-9]+")) {
 												int materialPoints = Integer.valueOf(event1.getName());
 												materialList.setPoints(materialPoints);
@@ -427,7 +439,7 @@ public class Levelling implements Listener {
 					materials = Materials.fromString(event.getCurrentItem().getType().name());
 				}
 
-				if (levellingManager.containsMaterials(materials)) {
+				if (levellingManager.containsMaterial(materials)) {
 					messageManager.sendMessage(player, configLoad.getString("Island.Admin.Levelling.Already.Message"));
 					soundManager.playSound(player, Sounds.ANVIL_LAND.bukkitSound(), 1.0F, 1.0F);