Address some code quality reports from SonarCloud.

Most of the errors are just sanity checks, as the most of null-pointers were already checked in other ways.

src/main/java/world/bentobox/challenges/commands/ChallengesGlobalPlayerCommand.java

@@ -19,7 +19,7 @@ import world.bentobox.challenges.utils.Utils;
 public class ChallengesGlobalPlayerCommand extends CompositeCommand
 {
 	/**
-	 * Constructor that inits command with given string.
+	 * Constructor that init command with given string.
 	 * @param addon Challenges Addon
 	 * @param gameModeAddons List with GameModes where challenges addon operates.
 	 */

src/main/java/world/bentobox/challenges/commands/CompleteChallengeCommand.java

@@ -16,7 +16,7 @@ import world.bentobox.challenges.utils.Utils;
 
 
 /**
- * This command allows to complete challenges without a gui.
+ * This command allows completing challenges without a gui.
  */
 public class CompleteChallengeCommand extends CompositeCommand
 {

src/main/java/world/bentobox/challenges/commands/admin/ChallengesAdminCommand.java

@@ -10,11 +10,11 @@ import world.bentobox.challenges.panel.admin.AdminPanel;
 
 public class ChallengesAdminCommand extends CompositeCommand
 {
-
     /**
-     * Admin command for challenges
+     * Instantiates a new Challenges' admin command.
      *
-     * @param parent
+     * @param addon the addon
+     * @param parent the parent
      */
     public ChallengesAdminCommand(ChallengesAddon addon, CompositeCommand parent)
     {

src/main/java/world/bentobox/challenges/commands/admin/ChallengesGlobalAdminCommand.java

@@ -6,7 +6,6 @@ import java.util.List;
 import world.bentobox.bentobox.api.addons.GameModeAddon;
 import world.bentobox.bentobox.api.commands.CompositeCommand;
 import world.bentobox.bentobox.api.user.User;
-import world.bentobox.bentobox.util.Util;
 import world.bentobox.challenges.ChallengesAddon;
 import world.bentobox.challenges.panel.user.GameModePanel;
 import world.bentobox.challenges.utils.Constants;
@@ -19,7 +18,7 @@ import world.bentobox.challenges.utils.Utils;
 public class ChallengesGlobalAdminCommand extends CompositeCommand
 {
 	/**
-	 * Constructor that inits command with given string.
+	 * Constructor that init command with given string.
 	 * @param addon Challenges Addon
 	 * @param gameModeAddons List with GameModes where challenges addon operates.
 	 */

src/main/java/world/bentobox/challenges/commands/admin/CompleteCommand.java

@@ -20,7 +20,7 @@ import world.bentobox.challenges.utils.Utils;
 
 
 /**
- * This command allows to complete challenges without a gui.
+ * This command allows completing challenges without a gui.
  */
 public class CompleteCommand extends CompositeCommand
 {
@@ -99,24 +99,26 @@ public class CompleteCommand extends CompositeCommand
 			// Add world name back at the start
 			String challengeName = Utils.getGameMode(this.getWorld()) + "_" + args.get(1);
 			Challenge challenge = this.addon.getChallengesManager().getChallenge(challengeName);
+			User target = User.getInstance(targetUUID);
 
-			if (challenge != null)
+			if (challenge != null && target != null)
 			{
 				if (!this.addon.getChallengesManager().isChallengeComplete(targetUUID, this.getWorld(), challenge))
 				{
 					this.addon.getChallengesManager().setChallengeComplete(
 						targetUUID, this.getWorld(), challenge, user.getUniqueId());
 
+
 					if (user.isPlayer())
 					{
 						Utils.sendMessage(user, user.getTranslation("challenges.messages.completed",
 							Constants.PARAMETER_NAME, challenge.getFriendlyName(),
-							Constants.PARAMETER_PLAYER, User.getInstance(targetUUID).getName()));
+							Constants.PARAMETER_PLAYER, target.getName()));
 					}
 					else
 					{
 						this.addon.log("Challenge " + challenge.getFriendlyName() + " completed for player " +
-							User.getInstance(targetUUID).getName());
+							target.getName());
 					}
 				}
 				else
@@ -166,23 +168,16 @@ public class CompleteCommand extends CompositeCommand
 
 		switch (size)
 		{
-			case 3:
+			case 3 ->
 				// Create suggestions with all challenges that is available for users.
-
 				returnList.addAll(Util.getOnlinePlayerList(user));
-				break;
+			case 4 ->
-			case 4:
 				// Create suggestions with all challenges that is available for users.
 				returnList.addAll(this.addon.getChallengesManager().getAllChallengesNames(this.getWorld()).stream().
 					map(challenge -> challenge.substring(Utils.getGameMode(this.getWorld()).length() + 1)).
 					collect(Collectors.toList()));
-
+			default ->
-				break;
-			default:
-			{
 				returnList.addAll(Collections.singletonList("help"));
-				break;
-			}
 		}
 
 		return Optional.of(Util.tabLimit(returnList, lastString));

src/main/java/world/bentobox/challenges/commands/admin/MigrateCommand.java

@@ -9,27 +9,32 @@ import world.bentobox.bentobox.api.user.User;
 import world.bentobox.challenges.ChallengesAddon;
 
 
-public class MigrateCommand extends CompositeCommand {
+public class MigrateCommand extends CompositeCommand
-
+{
     /**
-     * Migrates challenges
+     * Instantiates a new Migrate command command.
-     * @param addon
+     *
-     * @param cmd
+     * @param addon the addon
+     * @param cmd the cmd
      */
-    public MigrateCommand(Addon addon, CompositeCommand cmd) {
+    public MigrateCommand(Addon addon, CompositeCommand cmd)
+    {
         super(addon, cmd, "migrate");
     }
 
+
     @Override
-    public boolean execute(User user, String label, List<String> args) {
+    public boolean execute(User user, String label, List<String> args)
-        ((ChallengesAddon)getAddon()).getChallengesManager().migrateDatabase(user, getWorld());
+    {
+        ((ChallengesAddon) getAddon()).getChallengesManager().migrateDatabase(user, getWorld());
 
         return true;
     }
 
 
     @Override
-    public void setup() {
+    public void setup()
+    {
         this.setPermission("challenges.admin");
         this.setParametersHelp("challenges.commands.admin.migrate.parameters");
         this.setDescription("challenges.commands.admin.migrate.description");

src/main/java/world/bentobox/challenges/commands/admin/ReloadChallenges.java

@@ -11,13 +11,15 @@ import world.bentobox.challenges.utils.Utils;
 
 
 /**
- * This class allows to reload challenges addon.
+ * This class allows reloading challenges addon.
  */
 public class ReloadChallenges extends CompositeCommand
 {
     /**
-     * Admin command to reloads challenges addon.
+     * Instantiates a new Reload challenges command.
-     * @param parent
+     *
+     * @param addon the addon
+     * @param parent the parent
      */
     public ReloadChallenges(Addon addon, CompositeCommand parent)
     {
@@ -69,5 +71,8 @@ public class ReloadChallenges extends CompositeCommand
     // ---------------------------------------------------------------------
 
 
-    private ChallengesManager manager;
+    /**
+     * Addon Manager instance.
+     */
+    private final ChallengesManager manager;
 }

src/main/java/world/bentobox/challenges/commands/admin/ResetCommand.java

@@ -20,7 +20,7 @@ import world.bentobox.challenges.utils.Utils;
 
 
 /**
- * This command allows to reset challenges without a gui.
+ * This command allows resetting challenges without a gui.
  */
 public class ResetCommand extends CompositeCommand
 {
@@ -79,8 +79,9 @@ public class ResetCommand extends CompositeCommand
         else if (!args.get(1).isEmpty())
         {
             UUID targetUUID = this.getPlayers().getUUID(args.get(0));
+            User target = User.getInstance(targetUUID);
 
-            if (targetUUID == null)
+            if (targetUUID == null || target == null)
             {
                 if (user.isPlayer())
                 {
@@ -104,12 +105,11 @@ public class ResetCommand extends CompositeCommand
                 if (user.isPlayer())
                 {
                     Utils.sendMessage(user, user.getTranslation("challenges.messages.reset-all",
-                        Constants.PARAMETER_PLAYER, User.getInstance(targetUUID).getName()));
+                        Constants.PARAMETER_PLAYER, target.getName()));
                 }
                 else
                 {
-                    this.addon.log("All challenges for user " +
+                    this.addon.log("All challenges for user " + target.getName() + " was reset!");
-                        User.getInstance(targetUUID).getName() + " was reset!");
                 }
 
                 return true;
@@ -129,12 +129,12 @@ public class ResetCommand extends CompositeCommand
                         {
                             Utils.sendMessage(user, user.getTranslation("challenges.messages.reset",
                                 Constants.PARAMETER_NAME, challenge.getFriendlyName(),
-                                Constants.PARAMETER_PLAYER, User.getInstance(targetUUID).getName()));
+                                Constants.PARAMETER_PLAYER, target.getName()));
                         }
                         else
                         {
                             this.addon.log("Challenge " + challenge.getFriendlyName() + " was reset for player " +
-                                    User.getInstance(targetUUID).getName());
+                                target.getName());
                         }
                     }
                     else
@@ -185,25 +185,18 @@ public class ResetCommand extends CompositeCommand
 
         switch (size)
         {
-            case 3:
+            case 3 ->
                 // Create suggestions with all challenges that is available for users.
-
                 returnList.addAll(Util.getOnlinePlayerList(user));
-                break;
+            case 4 -> {
-            case 4:
                 // Create suggestions with all challenges that is available for users.
                 returnList.addAll(this.addon.getChallengesManager().getAllChallengesNames(this.getWorld()).stream().
                     map(challenge -> challenge.substring(Utils.getGameMode(this.getWorld()).length() + 1)).
                     collect(Collectors.toList()));
-
                 returnList.add("all");
-
-                break;
-            default:
-            {
-                returnList.addAll(Collections.singletonList("help"));
-                break;
             }
+            default ->
+                returnList.addAll(Collections.singletonList("help"));
         }
 
         return Optional.of(Util.tabLimit(returnList, lastString));
@@ -217,5 +210,5 @@ public class ResetCommand extends CompositeCommand
     /**
      * Variable that holds challenge addon. Single casting.
      */
-    private ChallengesAddon addon;
+    private final ChallengesAddon addon;
 }

src/main/java/world/bentobox/challenges/commands/admin/ShowChallenges.java

@@ -7,27 +7,32 @@ import world.bentobox.bentobox.api.commands.CompositeCommand;
 import world.bentobox.bentobox.api.user.User;
 import world.bentobox.challenges.ChallengesAddon;
 
-public class ShowChallenges extends CompositeCommand {
+public class ShowChallenges extends CompositeCommand
-
+{
-
     /**
-     * Admin command to show challenges and manage them
+     * Instantiates a new Show challenges command.
-     * @param parent
+     *
+     * @param addon the addon
+     * @param parent the parent
      */
-    public ShowChallenges(Addon addon, CompositeCommand parent) {
+    public ShowChallenges(Addon addon, CompositeCommand parent)
+    {
         super(addon, parent, "show");
     }
 
+
     @Override
-    public void setup() {
+    public void setup()
+    {
         this.setPermission("admin.challenges");
         this.setParametersHelp("challenges.commands.admin.show.parameters");
         this.setDescription("challenges.commands.admin.show.description");
-
     }
 
+
     @Override
-    public boolean execute(User user, String label, List<String> args) {
+    public boolean execute(User user, String label, List<String> args)
+    {
         if (user.isPlayer())
         {
             ((ChallengesAddon) getAddon()).getChallengesManager().
@@ -40,7 +45,5 @@ public class ShowChallenges extends CompositeCommand {
         }
 
         return true;
-
     }
-
 }

src/main/java/world/bentobox/challenges/database/object/Challenge.java

@@ -6,7 +6,6 @@ import java.util.stream.Collectors;
 
 import org.bukkit.Material;
 import org.bukkit.World;
-import org.bukkit.entity.EntityType;
 import org.bukkit.inventory.ItemStack;
 import org.eclipse.jdt.annotation.NonNull;
 
@@ -16,7 +15,6 @@ import com.google.gson.annotations.JsonAdapter;
 import world.bentobox.bentobox.BentoBox;
 import world.bentobox.bentobox.database.objects.DataObject;
 import world.bentobox.bentobox.database.objects.Table;
-import world.bentobox.challenges.database.object.adapters.EntityCompatibilityAdapter;
 import world.bentobox.challenges.database.object.adapters.RequirementsAdapter;
 import world.bentobox.challenges.database.object.adapters.TypeMigrationAdapter;
 import world.bentobox.challenges.database.object.requirements.Requirements;
@@ -838,7 +836,7 @@ public class Challenge implements DataObject
             clone.setEnvironment(new HashSet<>(this.environment));
             clone.setLevel(this.level);
             clone.setRemoveWhenCompleted(this.removeWhenCompleted);
-            clone.setRequirements(this.requirements.clone());
+            clone.setRequirements(this.requirements.copy());
             clone.setRewardText(this.rewardText);
             clone.setRewardItems(
                 this.rewardItems.stream().

src/main/java/world/bentobox/challenges/database/object/ChallengeLevel.java

@@ -6,6 +6,7 @@ import java.util.stream.Collectors;
 
 import org.bukkit.Material;
 import org.bukkit.inventory.ItemStack;
+import org.jetbrains.annotations.NotNull;
 
 import com.google.gson.annotations.Expose;
 
@@ -449,7 +450,7 @@ public class ChallengeLevel implements DataObject, Comparable<ChallengeLevel>
      * {@inheritDoc}
      */
     @Override
-    public int compareTo(ChallengeLevel o)
+    public int compareTo(@NotNull ChallengeLevel o)
     {
         if (this.equals(o))
         {
@@ -501,13 +502,11 @@ public class ChallengeLevel implements DataObject, Comparable<ChallengeLevel>
             return true;
         }
 
-        if (!(obj instanceof ChallengeLevel))
+        if (!(obj instanceof ChallengeLevel other))
         {
             return false;
         }
 
-        ChallengeLevel other = (ChallengeLevel) obj;
-
         if (uniqueId == null)
         {
             return other.uniqueId == null;
@@ -542,8 +541,7 @@ public class ChallengeLevel implements DataObject, Comparable<ChallengeLevel>
      * Clone method that returns clone of current challengeLevel.
      * @return ChallengeLevel that is cloned from current object.
      */
-    @Override
+    public ChallengeLevel copy()
-    public ChallengeLevel clone()
     {
         ChallengeLevel clone = new ChallengeLevel();
 

src/main/java/world/bentobox/challenges/database/object/ChallengesPlayerData.java

@@ -65,7 +65,7 @@ public class ChallengesPlayerData implements DataObject
     private Map<String, Integer> challengeStatus = new TreeMap<>(String.CASE_INSENSITIVE_ORDER);
 
     /**
-     * Map of challenges completion time where key is challenges unique id and value is
+     * Map of challenges completion time when key is challenges unique id and value is
      * timestamp when challenge was completed last time.
      */
     @Expose
@@ -353,13 +353,11 @@ public class ChallengesPlayerData implements DataObject
             return true;
         }
 
-        if (!(obj instanceof ChallengesPlayerData))
+        if (!(obj instanceof ChallengesPlayerData other))
         {
             return false;
         }
 
-        ChallengesPlayerData other = (ChallengesPlayerData) obj;
-
         if (uniqueId == null)
         {
             return other.uniqueId == null;

src/main/java/world/bentobox/challenges/database/object/adapters/EntityCompatibilityAdapter.java

@@ -33,10 +33,7 @@ public class EntityCompatibilityAdapter implements
 	{
 		JsonObject jsonArray = new JsonObject();
 
-		src.forEach((entity, number) ->
+		src.forEach((entity, number) -> jsonArray.addProperty(entity.name(), number));
-		{
-			jsonArray.addProperty(entity.name(), number);
-		});
 
 		return jsonArray;
 	}
@@ -46,7 +43,6 @@ public class EntityCompatibilityAdapter implements
 	 * This method deserializes json object that stores Entity Name and amount as integer.
 	 * @param json Json element that must be parsed.
 	 * @return EnumMap that contains EntityType as key and Integer as value.
-	 * @throws JsonParseException
 	 */
 	@Override
 	public Map<EntityType, Integer> deserialize(JsonElement json,

src/main/java/world/bentobox/challenges/database/object/adapters/TypeMigrationAdapter.java

@@ -42,7 +42,6 @@ public class TypeMigrationAdapter implements JsonSerializer<Challenge.ChallengeT
 
 		return switch (primitive.getAsString())
 		{
-			case "ISLAND", "ISLAND_TYPE" -> Challenge.ChallengeType.ISLAND_TYPE;
 			case "INVENTORY", "INVENTORY_TYPE" -> Challenge.ChallengeType.INVENTORY_TYPE;
 			case "OTHER", "OTHER_TYPE" -> Challenge.ChallengeType.OTHER_TYPE;
 			case "STATISTIC", "STATISTIC_TYPE" -> Challenge.ChallengeType.STATISTIC_TYPE;

src/main/java/world/bentobox/challenges/database/object/requirements/InventoryRequirements.java

@@ -126,12 +126,12 @@ public class InventoryRequirements extends Requirements
 
 
 	/**
-	 * Method Requirements#clone allows to clone Requirements object, to avoid changing content when it is necessary
+	 * Method Requirements#copy allows copies Requirements object, to avoid changing content when it is necessary
 	 * to use it.
-	 * @return InventoryRequirements clone
+	 * @return InventoryRequirements copy
 	 */
 	@Override
-	public Requirements clone()
+	public Requirements copy()
 	{
 		InventoryRequirements clone = new InventoryRequirements();
 		clone.setRequiredPermissions(new HashSet<>(this.getRequiredPermissions()));

src/main/java/world/bentobox/challenges/database/object/requirements/IslandRequirements.java

@@ -165,12 +165,12 @@ public class IslandRequirements extends Requirements
 
 
 	/**
-	 * Method Requirements#clone allows to clone Requirements object, to avoid changing content when it is necessary
+	 * Method Requirements#copy allows copies Requirements object, to avoid changing content when it is necessary
 	 * to use it.
-	 * @return IslandRequirements clone
+	 * @return IslandRequirements copy
 	 */
 	@Override
-	public Requirements clone()
+	public Requirements copy()
 	{
 		IslandRequirements clone = new IslandRequirements();
 		clone.setRequiredPermissions(new HashSet<>(this.getRequiredPermissions()));

src/main/java/world/bentobox/challenges/database/object/requirements/OtherRequirements.java

@@ -147,12 +147,12 @@ public class OtherRequirements extends Requirements
 
 
 	/**
-	 * Method Requirements#clone allows to clone Requirements object, to avoid changing content when it is necessary
+	 * Method Requirements#copy allows copies Requirements object, to avoid changing content when it is necessary
 	 * to use it.
-	 * @return OtherRequirements clone
+	 * @return OtherRequirements copy
 	 */
 	@Override
-	public Requirements clone()
+	public Requirements copy()
 	{
 		OtherRequirements clone = new OtherRequirements();
 		clone.setRequiredPermissions(new HashSet<>(this.getRequiredPermissions()));

src/main/java/world/bentobox/challenges/database/object/requirements/Requirements.java

@@ -70,12 +70,11 @@ public abstract class Requirements
 
 
 	/**
-	 * Method Requirements#clone allows to clone Requirements object, to avoid changing content when it is necessary
+	 * Method Requirements#copy allows to copy Requirements object, to avoid changing content when it is necessary
 	 * to use it.
-	 * @return Requirements clone
+	 * @return Requirements copy
 	 */
-	@Override
+	public abstract Requirements copy();
-	public abstract Requirements clone();
 
 
 // ---------------------------------------------------------------------

src/main/java/world/bentobox/challenges/database/object/requirements/StatisticRequirements.java

@@ -11,7 +11,6 @@ import com.google.gson.annotations.Expose;
 import org.bukkit.Material;
 import org.bukkit.Statistic;
 import org.bukkit.entity.EntityType;
-import org.eclipse.jdt.annotation.NonNull;
 import org.eclipse.jdt.annotation.Nullable;
 
 
@@ -27,11 +26,11 @@ public class StatisticRequirements extends Requirements
 
 
     /**
-     * This method clones given statistic object.
+     * This method copies given statistic object.
-     * @return Clone of this object.
+     * @return Copy of this object.
      */
     @Override
-    public Requirements clone()
+    public Requirements copy()
     {
         StatisticRequirements requirements = new StatisticRequirements();
         requirements.setStatistic(this.statistic);
@@ -96,7 +95,7 @@ public class StatisticRequirements extends Requirements
      *
      * @param statistic the statistic
      */
-    public void setStatistic(@NonNull Statistic statistic)
+    public void setStatistic(@Nullable Statistic statistic)
     {
         this.statistic = statistic;
     }

src/main/java/world/bentobox/challenges/handlers/ChallengeDataRequestHandler.java

@@ -101,5 +101,5 @@ public class ChallengeDataRequestHandler extends AddonRequestHandler
     /**
      * Variable stores challenges addon.
      */
-    private ChallengesAddon addon;
+    private final ChallengesAddon addon;
 }

src/main/java/world/bentobox/challenges/handlers/ChallengeListRequestHandler.java

@@ -5,6 +5,7 @@ import java.util.Collections;
 import java.util.Map;
 
 import org.bukkit.Bukkit;
+import org.bukkit.World;
 
 import world.bentobox.bentobox.api.addons.request.AddonRequestHandler;
 import world.bentobox.challenges.ChallengesAddon;
@@ -45,13 +46,19 @@ public class ChallengeListRequestHandler extends AddonRequestHandler
         if (metaData == null ||
             metaData.isEmpty() ||
             metaData.get("world-name") == null ||
-                !(metaData.get("world-name") instanceof String) ||
+            !(metaData.get("world-name") instanceof String))
-                Bukkit.getWorld((String) metaData.get("world-name")) == null)
         {
             return Collections.emptyList();
         }
 
-        return this.addon.getChallengesManager().getAllChallengesNames(Bukkit.getWorld((String) metaData.get("world-name")));
+        World world = Bukkit.getWorld((String) metaData.get("world-name"));
+
+        if (world == null)
+        {
+            return Collections.emptyList();
+        }
+
+        return this.addon.getChallengesManager().getAllChallengesNames(world);
     }
 
 
@@ -63,5 +70,5 @@ public class ChallengeListRequestHandler extends AddonRequestHandler
     /**
      * Variable stores challenges addon.
      */
-    private ChallengesAddon addon;
+    private final ChallengesAddon addon;
 }

src/main/java/world/bentobox/challenges/handlers/CompletedChallengesRequestHandler.java

@@ -54,14 +54,17 @@ public class CompletedChallengesRequestHandler extends AddonRequestHandler
             metaData.get("world-name") == null ||
             !(metaData.get("world-name") instanceof String) ||
             metaData.get("player") == null ||
-                !(metaData.get("player") instanceof UUID) ||
+            !(metaData.get("player") instanceof UUID player))
-                Bukkit.getWorld((String) metaData.get("world-name")) == null)
         {
             return Collections.emptySet();
         }
 
         World world = Bukkit.getWorld((String) metaData.get("world-name"));
-        UUID player = (UUID) metaData.get("player");
+
+        if (world == null)
+        {
+            return Collections.emptySet();
+        }
 
         ChallengesManager manager = this.addon.getChallengesManager();
 
@@ -79,5 +82,5 @@ public class CompletedChallengesRequestHandler extends AddonRequestHandler
     /**
      * Variable stores challenges addon.
      */
-    private ChallengesAddon addon;
+    private final ChallengesAddon addon;
 }

src/main/java/world/bentobox/challenges/handlers/LevelDataRequestHandler.java

@@ -94,5 +94,5 @@ public class LevelDataRequestHandler extends AddonRequestHandler
     /**
      * Variable stores challenges addon.
      */
-    private ChallengesAddon addon;
+    private final ChallengesAddon addon;
 }

src/main/java/world/bentobox/challenges/handlers/LevelListRequestHandler.java

@@ -5,6 +5,7 @@ import java.util.Collections;
 import java.util.Map;
 
 import org.bukkit.Bukkit;
+import org.bukkit.World;
 
 import world.bentobox.bentobox.api.addons.request.AddonRequestHandler;
 import world.bentobox.challenges.ChallengesAddon;
@@ -46,14 +47,19 @@ public class LevelListRequestHandler extends AddonRequestHandler
         if (metaData == null ||
             metaData.isEmpty() ||
             metaData.get("world-name") == null ||
-                !(metaData.get("world-name") instanceof String) ||
+            !(metaData.get("world-name") instanceof String))
-                Bukkit.getWorld((String) metaData.get("world-name")) == null)
         {
             return Collections.emptyList();
         }
 
-        return this.addon.getChallengesManager().getLevelNames(
+        World world = Bukkit.getWorld((String) metaData.get("world-name"));
-            Bukkit.getWorld((String) metaData.get("world-name")));
+
+        if (world == null)
+        {
+            return Collections.emptyList();
+        }
+
+        return this.addon.getChallengesManager().getLevelNames(world);
     }
 
 
@@ -65,5 +71,5 @@ public class LevelListRequestHandler extends AddonRequestHandler
     /**
      * Variable stores challenges addon.
      */
-    private ChallengesAddon addon;
+    private final ChallengesAddon addon;
 }

src/main/java/world/bentobox/challenges/listeners/SaveListener.java

@@ -50,5 +50,5 @@ public class SaveListener implements Listener
     // ---------------------------------------------------------------------
 
 
-    private ChallengesAddon addon;
+    private final ChallengesAddon addon;
 }

src/main/java/world/bentobox/challenges/managers/ChallengesImportManager.java

@@ -27,6 +27,7 @@ import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.annotations.Expose;
 
+import lv.id.bonne.panelutils.PanelUtils;
 import world.bentobox.bentobox.api.addons.GameModeAddon;
 import world.bentobox.bentobox.api.localization.TextVariables;
 import world.bentobox.bentobox.api.user.User;
@@ -661,14 +662,21 @@ public class ChallengesImportManager
      */
     public void importDatabaseFile(User user, World world, String fileName)
     {
+        World correctWorld = Util.getWorld(world);
+
+        if (correctWorld == null)
+        {
+            this.addon.logError("Given world is not part of BentoBox");
+            return;
+        }
+
         ChallengesManager manager = this.addon.getChallengesManager();
 
         // If exist any generator that is bound to current world, then do not load generators.
         if (manager.hasAnyChallengeData(world.getName()))
         {
-            this.addon.getPlugin().getIWM().getAddon(world).ifPresent(gameModeAddon -> {
+            this.addon.getPlugin().getIWM().getAddon(world).ifPresent(gameModeAddon ->
-                manager.wipeDatabase(gameModeAddon.getDescription().getName().toLowerCase());
+                manager.wipeDatabase(gameModeAddon.getDescription().getName().toLowerCase()));
-            });
         }
 
         try
@@ -700,7 +708,7 @@ public class ChallengesImportManager
                 // Set correct level ID
                 challengeLevel.setUniqueId(uniqueIDPrefix + challengeLevel.getUniqueId());
                 // Set correct world name
-                challengeLevel.setWorld(Util.getWorld(world).getName());
+                challengeLevel.setWorld(correctWorld.getName());
                 // Reset names for all challenges.
                 challengeLevel.setChallenges(challengeLevel.getChallenges().stream().
                     map(challenge -> uniqueIDPrefix + challenge).
@@ -728,6 +736,14 @@ public class ChallengesImportManager
      */
     public void loadDownloadedChallenges(User user, World world, String downloadString)
     {
+        World correctWorld = Util.getWorld(world);
+
+        if (correctWorld == null)
+        {
+            this.addon.logError("Given world is not part of BentoBox");
+            return;
+        }
+
         ChallengesManager manager = this.addon.getChallengesManager();
 
         // If exist any challenge or level that is bound to current world, then do not load default challenges.
@@ -769,7 +785,7 @@ public class ChallengesImportManager
                 // Set correct level ID
                 challengeLevel.setUniqueId(uniqueIDPrefix + challengeLevel.getUniqueId());
                 // Set correct world name
-                challengeLevel.setWorld(Util.getWorld(world).getName());
+                challengeLevel.setWorld(correctWorld.getName());
                 // Reset names for all challenges.
                 challengeLevel.setChallenges(challengeLevel.getChallenges().stream().
                         map(challenge -> uniqueIDPrefix + challenge).
@@ -840,7 +856,7 @@ public class ChallengesImportManager
                     stream().
                     map(challengeLevel -> {
                         // Use clone to avoid any changes in existing levels.
-                        ChallengeLevel clone = challengeLevel.clone();
+                        ChallengeLevel clone = challengeLevel.copy();
                         // Remove world name from level ID.
                         clone.setUniqueId(challengeLevel.getUniqueId().replaceFirst(replacementString, ""));
                         // Remove world name.

src/main/java/world/bentobox/challenges/managers/ChallengesManager.java

@@ -12,7 +12,6 @@ import org.bukkit.entity.EntityType;
 import org.eclipse.jdt.annotation.NonNull;
 import org.eclipse.jdt.annotation.Nullable;
 
-import world.bentobox.bentobox.api.addons.GameModeAddon;
 import world.bentobox.bentobox.api.logs.LogEntry;
 import world.bentobox.bentobox.api.user.User;
 import world.bentobox.bentobox.database.Database;
@@ -24,9 +23,6 @@ import world.bentobox.challenges.config.Settings;
 import world.bentobox.challenges.database.object.Challenge;
 import world.bentobox.challenges.database.object.ChallengeLevel;
 import world.bentobox.challenges.database.object.ChallengesPlayerData;
-import world.bentobox.challenges.database.object.requirements.InventoryRequirements;
-import world.bentobox.challenges.database.object.requirements.IslandRequirements;
-import world.bentobox.challenges.database.object.requirements.OtherRequirements;
 import world.bentobox.challenges.database.object.requirements.Requirements;
 import world.bentobox.challenges.events.ChallengeCompletedEvent;
 import world.bentobox.challenges.events.ChallengeResetAllEvent;
@@ -57,7 +53,7 @@ public class ChallengesManager
     private final Database<ChallengeLevel> levelDatabase;
 
     /**
-     * This database allows to access player challenge data.
+     * This database allows accessing player challenge data.
      */
     private final Database<ChallengesPlayerData> playersDatabase;
 
@@ -77,17 +73,17 @@ public class ChallengesManager
     private final Map<String, ChallengesPlayerData> playerCacheData;
 
     /**
-     * This variable allows to access ChallengesAddon.
+     * This variable allows accessing ChallengesAddon.
      */
     private final ChallengesAddon addon;
 
     /**
-     * This variable allows to access ChallengesAddon settings.
+     * This variable allows accessing ChallengesAddon settings.
      */
     private final Settings settings;
 
     /**
-     * Island world manager allows to detect which world refferes to which gamemode addon.
+     * Island world manager allows detecting which world refers to which gamemode addon.
      */
     private final IslandWorldManager islandWorldManager;
 
@@ -121,7 +117,7 @@ public class ChallengesManager
         {
             if (o1.getOrder() == o2.getOrder())
             {
-                // If orders are equal, sort by unique Id
+                // If orders are equal, sort by unique id
                 return o1.getUniqueId().compareToIgnoreCase(o2.getUniqueId());
             }
             else
@@ -138,10 +134,19 @@ public class ChallengesManager
                 return Boolean.compare(o2.getLevel().isEmpty(), o1.getLevel().isEmpty());
             }
             else
+            {
+                ChallengeLevel o1Level = this.getLevel(o1.getLevel());
+                ChallengeLevel o2Level = this.getLevel(o2.getLevel());
+
+                if (o1Level == null || o2Level == null)
+                {
+                    return Boolean.compare(o1Level == null, o2Level == null);
+                }
+                else
                 {
                     // Sort by challenges level order numbers
-                return Integer.compare(this.getLevel(o1.getLevel()).getOrder(),
+                    return Integer.compare(o1Level.getOrder(), o2Level.getOrder());
-                        this.getLevel(o2.getLevel()).getOrder());
+                }
             }
         }
     };
@@ -166,7 +171,7 @@ public class ChallengesManager
         // Set up the configs
         this.challengeDatabase = new Database<>(addon, Challenge.class);
         this.levelDatabase = new Database<>(addon, ChallengeLevel.class);
-        // Players is where all the player history will be stored
+        // playersDatabase is where all the player history will be stored
         this.playersDatabase = new Database<>(addon, ChallengesPlayerData.class);
 
         // Init all cache objects.
@@ -226,9 +231,10 @@ public class ChallengesManager
             // store player data before cleaning.
             this.savePlayersData();
         }
-        //this.challengeDatabase = new Database<>(addon, Challenge.class);
+
-        //this.levelDatabase = new Database<>(addon, ChallengeLevel.class);
+        // this.challengeDatabase = new Database<>(addon, Challenge.class);
-        //this.playersDatabase = new Database<>(addon, ChallengesPlayerData.class);
+        // this.levelDatabase = new Database<>(addon, ChallengeLevel.class);
+        // this.playersDatabase = new Database<>(addon, ChallengesPlayerData.class);
 
         this.loadAndValidate();
     }
@@ -420,26 +426,6 @@ public class ChallengesManager
     }
 
 
-    /**
-     * This method stores PlayerData into local cache.
-     *
-     * @param playerData ChallengesPlayerData that must be loaded.
-     *
-     * TODO: Remove this unused method?
-     */
-    private void loadPlayerData(@NonNull ChallengesPlayerData playerData)
-    {
-        try
-        {
-            this.playerCacheData.put(playerData.getUniqueId(), playerData);
-        }
-        catch (Exception e)
-        {
-            this.addon.getLogger().severe("UUID for player in challenge data file is invalid!");
-        }
-    }
-
-
     /**
      * This method removes given player from cache data.
      *

src/main/java/world/bentobox/challenges/panel/CommonPanel.java

@@ -528,11 +528,9 @@ public abstract class CommonPanel
 
         switch (requirement.getStatistic().getType())
         {
-            case UNTYPED -> {
+            case UNTYPED -> statistic = this.user.getTranslationOrNothing(reference + "statistic",
-                statistic = this.user.getTranslationOrNothing(reference + "statistic",
                 "[statistic]", Utils.prettifyObject(requirement.getStatistic(), this.user),
                 "[number]", String.valueOf(requirement.getAmount()));
-            }
             case ITEM, BLOCK -> {
                 if (requirement.getAmount() > 1)
                 {
@@ -563,9 +561,7 @@ public abstract class CommonPanel
                         "[target]", Utils.prettifyObject(requirement.getEntity(), this.user));
                 }
             }
-            default -> {
+            default -> statistic = "";
-                statistic = "";
-            }
         }
 
         String warning = requirement.isReduceStatistic() ?

src/main/java/world/bentobox/challenges/panel/ConversationUtils.java

@@ -77,7 +77,6 @@ public class ConversationUtils
              * @return the prompt
              */
             @Override
-            @Nullable
             protected Prompt acceptValidatedInput(@NotNull ConversationContext context, @NotNull String input)
             {
                 String validEntry = user.getTranslation(Constants.CONVERSATIONS + "confirm-string").toLowerCase();
@@ -105,7 +104,8 @@ public class ConversationUtils
              * @see Prompt#getPromptText(ConversationContext)
              */
             @Override
-            public @NotNull String getPromptText(@NotNull ConversationContext conversationContext)
+            @NotNull
+            public String getPromptText(@NotNull ConversationContext conversationContext)
             {
                 // Close input GUI.
                 user.closeInventory();
@@ -154,7 +154,8 @@ public class ConversationUtils
              * @return The text to display.
              */
             @Override
-            public String getPromptText(ConversationContext context)
+            @NotNull
+            public String getPromptText(@NotNull ConversationContext context)
             {
                 // Close input GUI.
                 user.closeInventory();
@@ -175,7 +176,7 @@ public class ConversationUtils
              * validity of the input.
              */
             @Override
-            protected boolean isInputValid(ConversationContext context, String input)
+            protected boolean isInputValid(@NotNull ConversationContext context, @NotNull String input)
             {
                 return validation.apply(input);
             }
@@ -194,8 +195,8 @@ public class ConversationUtils
              * correct the input.
              */
             @Override
-            protected String getFailedValidationText(ConversationContext context,
+            protected String getFailedValidationText(@NotNull ConversationContext context,
-                    String invalidInput)
+                @NotNull String invalidInput)
             {
                 return user.getTranslation(failTranslationLocation,
                         Constants.PARAMETER_ID,
@@ -216,7 +217,7 @@ public class ConversationUtils
              * @return The next Prompt in the prompt graph.
              */
             @Override
-            protected Prompt acceptValidatedInput(ConversationContext context, String input)
+            protected Prompt acceptValidatedInput(@NotNull ConversationContext context, @NotNull String input)
             {
                 // Add answer to consumer.
                 consumer.accept(input);
@@ -267,7 +268,7 @@ public class ConversationUtils
              * graph.
              */
             @Override
-            protected Prompt acceptValidatedInput(ConversationContext context, Number input)
+            protected Prompt acceptValidatedInput(@NotNull ConversationContext context, @NotNull Number input)
             {
                 // Add answer to consumer.
                 consumer.accept(input);
@@ -285,7 +286,7 @@ public class ConversationUtils
              * @return The validity of the player's input.
              */
             @Override
-            protected boolean isNumberValid(ConversationContext context, Number input)
+            protected boolean isNumberValid(@NotNull ConversationContext context, Number input)
             {
                 return input.doubleValue() >= minValue.doubleValue() &&
                         input.doubleValue() <= maxValue.doubleValue();
@@ -301,7 +302,7 @@ public class ConversationUtils
              * @return A message explaining how to correct the input.
              */
             @Override
-            protected String getInputNotNumericText(ConversationContext context, String invalidInput)
+            protected String getInputNotNumericText(@NotNull ConversationContext context, @NotNull String invalidInput)
             {
                 return user.getTranslation(Constants.CONVERSATIONS + "numeric-only", Constants.PARAMETER_VALUE, invalidInput);
             }
@@ -316,7 +317,7 @@ public class ConversationUtils
              * @return A message explaining how to correct the input.
              */
             @Override
-            protected String getFailedValidationText(ConversationContext context, Number invalidInput)
+            protected String getFailedValidationText(@NotNull ConversationContext context, Number invalidInput)
             {
                 return user.getTranslation(Constants.CONVERSATIONS + "not-valid-value",
                         Constants.PARAMETER_VALUE, invalidInput.toString(),
@@ -329,7 +330,8 @@ public class ConversationUtils
              * @see Prompt#getPromptText(ConversationContext)
              */
             @Override
-            public String getPromptText(ConversationContext conversationContext)
+            @NotNull
+            public String getPromptText(@NotNull ConversationContext conversationContext)
             {
                 // Close input GUI.
                 user.closeInventory();
@@ -373,13 +375,12 @@ public class ConversationUtils
         MessagePrompt messagePrompt = new MessagePrompt()
         {
             @Override
-            public @NotNull String getPromptText(@NotNull ConversationContext context)
+            @NotNull
+            public String getPromptText(@NotNull ConversationContext context)
             {
-                List<String> description = (List<String>) context.getSessionData(SESSION_CONSTANT);
+                if (context.getSessionData(SESSION_CONSTANT) instanceof List description)
-
-                if (description != null)
                 {
-                    consumer.accept(description);
+                    consumer.accept((List<String>) description);
                     return successMessage;
                 }
                 else
@@ -400,7 +401,8 @@ public class ConversationUtils
         StringPrompt stringPrompt = new StringPrompt()
         {
             @Override
-            public @NotNull String getPromptText(@NotNull ConversationContext context)
+            @NotNull
+            public String getPromptText(@NotNull ConversationContext context)
             {
                 user.closeInventory();
 
@@ -424,7 +426,7 @@ public class ConversationUtils
 
 
             @Override
-            public @Nullable Prompt acceptInput(@NotNull ConversationContext context, @Nullable String input)
+            public Prompt acceptInput(@NotNull ConversationContext context, @Nullable String input)
             {
                 String[] exit = user.getTranslation(Constants.CONVERSATIONS + "exit-string").
                         toLowerCase().replaceAll("\\s", "").
@@ -437,9 +439,9 @@ public class ConversationUtils
 
                 List<String> desc = new ArrayList<>();
 
-                if (context.getSessionData(SESSION_CONSTANT) != null)
+                if (context.getSessionData(SESSION_CONSTANT) instanceof List list)
                 {
-                    desc = ((List<String>) context.getSessionData(SESSION_CONSTANT));
+                    desc = (List<String>) list;
                 }
                 if (input != null) {
                     desc.add(ChatColor.translateAlternateColorCodes('&', input));
@@ -479,7 +481,8 @@ public class ConversationUtils
         StringPrompt stringPrompt = new StringPrompt()
         {
             @Override
-            public @NotNull String getPromptText(@NotNull ConversationContext context)
+            @NotNull
+            public String getPromptText(@NotNull ConversationContext context)
             {
                 user.closeInventory();
                 return question;
@@ -487,7 +490,8 @@ public class ConversationUtils
 
 
             @Override
-            public @NotNull Prompt acceptInput(@NotNull ConversationContext context, @Nullable String input)
+            @NotNull
+            public Prompt acceptInput(@NotNull ConversationContext context, @Nullable String input)
             {
                 consumer.accept(input);
                 return ConversationUtils.endMessagePrompt(successMessage);
@@ -519,14 +523,16 @@ public class ConversationUtils
         return new MessagePrompt()
         {
             @Override
-            public @NotNull String getPromptText(@NotNull ConversationContext context)
+            @NotNull
+            public String getPromptText(@NotNull ConversationContext context)
             {
                 return message == null ? "" : message;
             }
 
 
             @Override
-            protected @Nullable Prompt getNextPrompt(@NotNull ConversationContext context)
+            @Nullable
+            protected Prompt getNextPrompt(@NotNull ConversationContext context)
             {
                 return Prompt.END_OF_CONVERSATION;
             }

src/main/java/world/bentobox/challenges/panel/admin/ManageBlocksPanel.java

@@ -158,10 +158,9 @@ public class ManageBlocksPanel extends CommonPagedPanel<Material>
 				if (!this.selectedMaterials.isEmpty())
 				{
 					description.add(this.user.getTranslation(reference + "title"));
-					this.selectedMaterials.forEach(material -> {
+					this.selectedMaterials.forEach(material ->
 						description.add(this.user.getTranslation(reference + "material",
-							"[material]", Utils.prettifyObject(material, this.user)));
+							"[material]", Utils.prettifyObject(material, this.user))));
-					});
 				}
 
 				icon = new ItemStack(Material.LAVA_BUCKET);

src/main/java/world/bentobox/challenges/panel/admin/ManageEntitiesPanel.java

@@ -155,10 +155,9 @@ public class ManageEntitiesPanel extends CommonPagedPanel<EntityType>
 				if (!this.selectedEntities.isEmpty())
 				{
 					description.add(this.user.getTranslation(reference + "title"));
-					this.selectedEntities.forEach(entity -> {
+					this.selectedEntities.forEach(entity ->
 						description.add(this.user.getTranslation(reference + "entity",
-							"[entity]", Utils.prettifyObject(entity, this.user)));
+							"[entity]", Utils.prettifyObject(entity, this.user))));
-					});
 				}
 
 				icon = new ItemStack(Material.LAVA_BUCKET);

src/main/java/world/bentobox/challenges/panel/util/ChallengeSelector.java

@@ -120,10 +120,9 @@ public class ChallengeSelector extends PagedSelector<Challenge>
 				if (!this.selectedElements.isEmpty())
 				{
 					description.add(this.user.getTranslation(reference + "title"));
-					this.selectedElements.forEach(challenge -> {
+					this.selectedElements.forEach(challenge ->
 						description.add(this.user.getTranslation(reference + "element",
-							"[element]", challenge.getFriendlyName()));
+							"[element]", challenge.getFriendlyName())));
-					});
 				}
 
 				icon = new ItemStack(Material.COMMAND_BLOCK);

src/main/java/world/bentobox/challenges/panel/util/EnvironmentSelector.java

@@ -143,10 +143,9 @@ public record EnvironmentSelector(User user, Set<World.Environment> values, BiCo
 				if (!this.values.isEmpty())
 				{
 					description.add(this.user.getTranslation(reference + "title"));
-					this.values.forEach(element -> {
+					this.values.forEach(element ->
 						description.add(this.user.getTranslation(reference + "element",
-							"[element]", Utils.prettifyObject(element, this.user)));
+							"[element]", Utils.prettifyObject(element, this.user))));
-					});
 				}
 
 				icon = new ItemStack(Material.COMMAND_BLOCK);

src/main/java/world/bentobox/challenges/panel/util/MultiBlockSelector.java

@@ -160,10 +160,9 @@ public class MultiBlockSelector extends PagedSelector<Material>
 				if (!this.selectedElements.isEmpty())
 				{
 					description.add(this.user.getTranslation(reference + "title"));
-					this.selectedElements.forEach(material -> {
+					this.selectedElements.forEach(material ->
 						description.add(this.user.getTranslation(reference + "element",
-							"[element]", Utils.prettifyObject(material, this.user)));
+							"[element]", Utils.prettifyObject(material, this.user))));
-					});
 				}
 
 				icon = new ItemStack(Material.COMMAND_BLOCK);

src/main/java/world/bentobox/challenges/panel/util/MultiEntitySelector.java

@@ -144,10 +144,9 @@ public class MultiEntitySelector extends PagedSelector<EntityType>
 				if (!this.selectedElements.isEmpty())
 				{
 					description.add(this.user.getTranslation(reference + "title"));
-					this.selectedElements.forEach(material -> {
+					this.selectedElements.forEach(material ->
 						description.add(this.user.getTranslation(reference + "element",
-							"[element]", Utils.prettifyObject(material, this.user)));
+							"[element]", Utils.prettifyObject(material, this.user))));
-					});
 				}
 
 				icon = new ItemStack(Material.COMMAND_BLOCK);

src/main/java/world/bentobox/challenges/tasks/TryToComplete.java

@@ -4,7 +4,6 @@ package world.bentobox.challenges.tasks;
 
 import com.google.common.collect.UnmodifiableIterator;
 import java.time.*;
-import java.time.temporal.ChronoUnit;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.EnumMap;
@@ -61,7 +60,7 @@ public class TryToComplete
     /**
      * Challenges addon variable.
      */
-    private ChallengesAddon addon;
+    private final ChallengesAddon addon;
 
     /**
      * Challenges manager for addon.
@@ -83,11 +82,6 @@ public class TryToComplete
      */
     private String permissionPrefix;
 
-    /**
-     * Top command first label.
-     */
-    private String topLabel;
-
     /**
      * Challenge that should be completed.
      */
@@ -102,13 +96,6 @@ public class TryToComplete
     // Section: Builder
     // ---------------------------------------------------------------------
 
-    @Deprecated
-    public TryToComplete label(String label)
-    {
-        this.topLabel = label;
-        return this;
-    }
-
 
     @Deprecated
     public TryToComplete user(User user)
@@ -118,38 +105,6 @@ public class TryToComplete
     }
 
 
-    @Deprecated
-    public TryToComplete manager(ChallengesManager manager)
-    {
-        this.manager = manager;
-        return this;
-    }
-
-
-    @Deprecated
-    public TryToComplete challenge(Challenge challenge)
-    {
-        this.challenge = challenge;
-        return this;
-    }
-
-
-    @Deprecated
-    public TryToComplete world(World world)
-    {
-        this.world = world;
-        return this;
-    }
-
-
-    @Deprecated
-    public TryToComplete permPrefix(String prefix)
-    {
-        this.permissionPrefix = prefix;
-        return this;
-    }
-
-
     @Deprecated
     public TryToComplete(ChallengesAddon addon)
     {
@@ -185,7 +140,6 @@ public class TryToComplete
         // To avoid any modifications that may occur to challenges in current completion
         // just clone it.
         this.challenge = challenge.clone();
-        this.topLabel = topLabel;
     }
 
 
@@ -254,6 +208,13 @@ public class TryToComplete
             return result;
         }
 
+        if (this.user.getLocation() == null || this.user.getInventory() == null)
+        {
+            // This is just a cleaning check. There is no situations where location or inventory
+            // could be null at this point of code.
+            return result;
+        }
+
         this.fullFillRequirements(result);
 
         // Validation to avoid rewarding if something goes wrong in removing requirements.
@@ -314,12 +275,10 @@ public class TryToComplete
                     filter(player -> this.user.getUniqueId().equals(player.getUniqueId())).
                     map(User::getInstance).
                     filter(Objects::nonNull).
-                    forEach(user -> {
+                    forEach(user -> Utils.sendMessage(user, user.getTranslation(
-                        Utils.sendMessage(user, user.getTranslation(
                         "challenges.messages.name-has-completed-challenge",
                         Constants.PARAMETER_NAME, this.user.getName(),
-                            "[value]", this.challenge.getFriendlyName()));
+                        "[value]", this.challenge.getFriendlyName())));
-                    });
             }
 
             // sends title to player on challenge completion
@@ -355,7 +314,7 @@ public class TryToComplete
             if (this.addon.isEconomyProvided())
             {
                 this.addon.getEconomyProvider().deposit(this.user,
-                        (double)this.challenge.getRepeatMoneyReward() * rewardFactor);
+                    this.challenge.getRepeatMoneyReward() * rewardFactor);
             }
 
             // Experience Repeat Reward
@@ -424,12 +383,10 @@ public class TryToComplete
                             filter(player -> this.user.getUniqueId().equals(player.getUniqueId())).
                             map(User::getInstance).
                             filter(Objects::nonNull).
-                            forEach(user -> {
+                            forEach(user -> Utils.sendMessage(user, user.getTranslation(
-                                Utils.sendMessage(user, user.getTranslation(
                                 "challenges.messages.name-has-completed-level",
                                 Constants.PARAMETER_NAME, this.user.getName(),
-                                    "[value]", level.getFriendlyName()));
+                                "[value]", level.getFriendlyName())));
-                            });
                     }
 
                     this.manager.setLevelComplete(this.user, this.world, level);
@@ -453,7 +410,7 @@ public class TryToComplete
 
 
     /**
-     * This method full fills all challenge type requirements, that is not full filled yet.
+     * This method fulfills all challenge type requirements, that is not fulfilled yet.
      * @param result Challenge Results
      */
     private void fullFillRequirements(ChallengeResult result)
@@ -520,7 +477,7 @@ public class TryToComplete
             case STATISTIC_TYPE -> {
                 StatisticRequirements requirements = this.challenge.getRequirements();
 
-                if (requirements.isReduceStatistic())
+                if (requirements.isReduceStatistic() && requirements.getStatistic() != null)
                 {
                     int removeAmount = result.getFactor() * requirements.getAmount();
 
@@ -544,7 +501,12 @@ public class TryToComplete
                         case ITEM, BLOCK -> {
                             int statistic = this.user.getPlayer().getStatistic(requirements.getStatistic());
 
-                            if (removeAmount >= statistic)
+                            if (requirements.getMaterial() == null)
+                            {
+                                // Just a sanity check. Material cannot be null at this point of code.
+                                removeAmount = 0;
+                            }
+                            else if (removeAmount >= statistic)
                             {
                                 this.user.getPlayer().setStatistic(requirements.getStatistic(), requirements.getMaterial(), 0);
                                 removeAmount -= statistic;
@@ -560,7 +522,12 @@ public class TryToComplete
                         case ENTITY -> {
                             int statistic = this.user.getPlayer().getStatistic(requirements.getStatistic());
 
-                            if (removeAmount >= statistic)
+                            if (requirements.getEntity() == null)
+                            {
+                                // Just a sanity check. Entity cannot be null at this point of code.
+                                removeAmount = 0;
+                            }
+                            else if (removeAmount >= statistic)
                             {
                                 this.user.getPlayer().setStatistic(requirements.getStatistic(), requirements.getEntity(), 0);
                                 removeAmount -= statistic;
@@ -616,7 +583,12 @@ public class TryToComplete
                                 case ITEM, BLOCK -> {
                                     int statistic = player.getStatistic(requirements.getStatistic());
 
-                                    if (removeAmount >= statistic)
+                                    if (requirements.getMaterial() == null)
+                                    {
+                                        // Just a sanity check. Entity cannot be null at this point of code.
+                                        removeAmount = 0;
+                                    }
+                                    else if (removeAmount >= statistic)
                                     {
                                         removeAmount -= statistic;
                                         player.setStatistic(requirements.getStatistic(), requirements.getMaterial(), 0);
@@ -632,7 +604,12 @@ public class TryToComplete
                                 case ENTITY -> {
                                     int statistic = player.getStatistic(requirements.getStatistic());
 
-                                    if (removeAmount >= statistic)
+                                    if (requirements.getEntity() == null)
+                                    {
+                                        // Just a sanity check. Entity cannot be null at this point of code.
+                                        removeAmount = 0;
+                                    }
+                                    else if (removeAmount >= statistic)
                                     {
                                         removeAmount -= statistic;
                                         player.setStatistic(requirements.getStatistic(), requirements.getEntity(), 0);
@@ -682,7 +659,8 @@ public class TryToComplete
             result = EMPTY_RESULT;
         }
         // Player is not on island
-        else if (ChallengesAddon.CHALLENGES_WORLD_PROTECTION.isSetForWorld(this.world) &&
+        else if (this.user.getLocation() == null ||
+            ChallengesAddon.CHALLENGES_WORLD_PROTECTION.isSetForWorld(this.world) &&
                 !this.addon.getIslands().locationIsOnIsland(this.user.getPlayer(), this.user.getLocation()))
         {
             Utils.sendMessage(this.user, this.user.getTranslation("challenges.errors.not-on-island"));
@@ -827,7 +805,7 @@ public class TryToComplete
             {
                 String alert = "Running command '" + cmd + "' as " + this.user.getName();
                 this.addon.getLogger().info(alert);
-                cmd = cmd.substring(6, cmd.length()).replace(Constants.PARAMETER_PLAYER, this.user.getName()).trim();
+                cmd = cmd.substring(6).replace(Constants.PARAMETER_PLAYER, this.user.getName()).trim();
                 try
                 {
                     if (!user.performCommand(cmd))
@@ -896,7 +874,12 @@ public class TryToComplete
             {
                 int numInInventory;
 
-                if (this.getInventoryRequirements().getIgnoreMetaData().contains(required.getType()))
+                if (this.user.getInventory() == null)
+                {
+                    // Sanity check. User always has inventory at this point of code.
+                    numInInventory = 0;
+                }
+                else if (this.getInventoryRequirements().getIgnoreMetaData().contains(required.getType()))
                 {
                     numInInventory = Arrays.stream(this.user.getInventory().getContents()).
                         filter(Objects::nonNull).
@@ -951,7 +934,12 @@ public class TryToComplete
             int amountToBeRemoved = required.getAmount() * factor;
             List<ItemStack> itemsInInventory;
 
-            if (this.getInventoryRequirements().getIgnoreMetaData().contains(required.getType()))
+            if (this.user.getInventory() == null)
+            {
+                // Sanity check. User always has inventory at this point of code.
+                itemsInInventory = Collections.emptyList();
+            }
+            else if (this.getInventoryRequirements().getIgnoreMetaData().contains(required.getType()))
             {
                 // Use collecting method that ignores item meta.
                 itemsInInventory = Arrays.stream(user.getInventory().getContents()).
@@ -1069,10 +1057,10 @@ public class TryToComplete
                 boundingBox.getHeight() > distance * 2 + 3)
             {
                 this.addon.logError("BoundingBox is larger than SearchRadius. " +
-                        " | BoundingBox: " + boundingBox.toString() +
+                        " | BoundingBox: " + boundingBox +
                         " | Search Distance: " + requirements.getSearchRadius() +
-                        " | Location: " + this.user.getLocation().toString() +
+                        " | Location: " + this.user.getLocation() +
-                        " | Center: " + island.getCenter().toString() +
+                        " | Center: " + island.getCenter() +
                         " | Range: " + range);
 
                 return EMPTY_RESULT;
@@ -1110,7 +1098,7 @@ public class TryToComplete
 
         // This queue will contain only blocks whit required type ordered by distance till player.
         Queue<Block> blockFromWorld = new PriorityQueue<>((o1, o2) -> {
-            if (o1.getType().equals(o2.getType()))
+            if (o1.getType().equals(o2.getType()) && this.user.getLocation() != null)
             {
                 return Double.compare(o1.getLocation().distance(this.user.getLocation()),
                     o2.getLocation().distance(this.user.getLocation()));
@@ -1210,7 +1198,7 @@ public class TryToComplete
 
         // Create queue that contains all required entities ordered by distance till player.
         Queue<Entity> entityQueue = new PriorityQueue<>((o1, o2) -> {
-            if (o1.getType().equals(o2.getType()))
+            if (o1.getType().equals(o2.getType()) && this.user.getLocation() != null)
             {
                 return Double.compare(o1.getLocation().distance(this.user.getLocation()),
                     o2.getLocation().distance(this.user.getLocation()));
@@ -1408,6 +1396,12 @@ public class TryToComplete
 
         int currentValue;
 
+        if (requirements.getStatistic() == null)
+        {
+            // Sanity check.
+            return EMPTY_RESULT;
+        }
+
         switch (requirements.getStatistic().getType())
         {
             case UNTYPED -> currentValue =
@@ -1454,7 +1448,10 @@ public class TryToComplete
         if (inputMessage.contains("[") && inputMessage.contains("]"))
         {
             outputMessage = outputMessage.replace("[friendlyName]", challenge.getFriendlyName());
-            outputMessage = outputMessage.replace("[level]", challenge.getLevel().isEmpty() ? "" : this.manager.getLevel(challenge.getLevel()).getFriendlyName());
+
+            ChallengeLevel level = challenge.getLevel().isEmpty() ? null : this.manager.getLevel(challenge.getLevel());
+            outputMessage = outputMessage.replace("[level]", level == null ? "" : level.getFriendlyName());
+
             outputMessage = outputMessage.replace("[rewardText]", challenge.getRewardText());
         }
 

src/main/java/world/bentobox/challenges/utils/LevelStatus.java

@@ -19,7 +19,7 @@ public class LevelStatus {
      * @param previousLevel - previous level
      * @param numberOfChallengesStillToDo - number of challenges still to do on this level
      * @param complete - whether complete or not
-     * @param isUnlocked 
+     * @param isUnlocked - if level is unlocked or not.
      */
     public LevelStatus(ChallengeLevel level, ChallengeLevel previousLevel, int numberOfChallengesStillToDo, boolean complete, boolean isUnlocked) {
         super();

src/main/java/world/bentobox/challenges/utils/Utils.java

@@ -63,7 +63,7 @@ public class Utils
 				i++;
 			}
 
-			if (isUnique && item != null)
+			if (isUnique)
 			{
 				// The same issue as in other places. Clone prevents from changing original item.
 				returnItems.add(item.clone());
@@ -95,7 +95,7 @@ public class Utils
 	 * @param <T> Instance of given object.
 	 * @return Next value after currentValue in values array.
 	 */
-	public static <T extends Object> T getNextValue(T[] values, T currentValue)
+	public static <T> T getNextValue(T[] values, T currentValue)
 	{
 		for (int i = 0; i < values.length; i++)
 		{
@@ -123,7 +123,7 @@ public class Utils
 	 * @param <T> Instance of given object.
 	 * @return Previous value before currentValue in values array.
 	 */
-	public static <T extends Object> T getPreviousValue(T[] values, T currentValue)
+	public static <T> T getPreviousValue(T[] values, T currentValue)
 	{
 		for (int i = 0; i < values.length; i++)
 		{
@@ -544,19 +544,15 @@ public class Utils
 		String translation;
 		switch (object.getType())
 		{
-			case POTION, SPLASH_POTION, LINGERING_POTION, TIPPED_ARROW -> {
+			case POTION, SPLASH_POTION, LINGERING_POTION, TIPPED_ARROW ->
 				// Get Potion Meta
 				translation = prettifyObject(object, (PotionMeta) object.getItemMeta(), user);
-			}
+			case PLAYER_HEAD, PLAYER_WALL_HEAD ->
-			case PLAYER_HEAD, PLAYER_WALL_HEAD -> {
 				translation = prettifyObject(object, (SkullMeta) object.getItemMeta(), user);
-			}
+			case ENCHANTED_BOOK ->
-			case ENCHANTED_BOOK -> {
 				translation = prettifyObject(object, (EnchantmentStorageMeta) object.getItemMeta(), user);
-			}
+			case WRITTEN_BOOK, WRITABLE_BOOK ->
-			case WRITTEN_BOOK, WRITABLE_BOOK -> {
 				translation = prettifyObject(object, (BookMeta) object.getItemMeta(), user);
-			}
 			case LEATHER_BOOTS,LEATHER_CHESTPLATE,LEATHER_HELMET,LEATHER_LEGGINGS,LEATHER_HORSE_ARMOR,
 				TRIDENT,CROSSBOW,CHAINMAIL_HELMET,CHAINMAIL_CHESTPLATE,CHAINMAIL_LEGGINGS,CHAINMAIL_BOOTS,IRON_HELMET,
 				IRON_CHESTPLATE,IRON_LEGGINGS,IRON_BOOTS,DIAMOND_HELMET,DIAMOND_CHESTPLATE,DIAMOND_LEGGINGS,DIAMOND_BOOTS,
@@ -565,9 +561,8 @@ public class Utils
 				STONE_SWORD,STONE_SHOVEL,STONE_PICKAXE,STONE_AXE,STONE_HOE,GOLDEN_SWORD,GOLDEN_SHOVEL,GOLDEN_PICKAXE,
 				GOLDEN_AXE,GOLDEN_HOE,IRON_SWORD,IRON_SHOVEL,IRON_PICKAXE,IRON_AXE,IRON_HOE,DIAMOND_SWORD,DIAMOND_SHOVEL,
 				DIAMOND_PICKAXE,DIAMOND_AXE,DIAMOND_HOE,NETHERITE_SWORD,NETHERITE_SHOVEL,NETHERITE_PICKAXE,NETHERITE_AXE,
-				NETHERITE_HOE,TURTLE_HELMET,SHEARS,SHIELD,FLINT_AND_STEEL,BOW -> {
+				NETHERITE_HOE,TURTLE_HELMET,SHEARS,SHIELD,FLINT_AND_STEEL,BOW ->
 				translation = prettifyObject(object, object.getItemMeta(), user);
-			}
 			default ->
 				translation = "";
 		}