Address SonarCloud findings on #419

- S1192: extract the duplicated "click-to-add" literal into
  Constants.CLICK_TO_ADD and use it in all three spots.
- S6204: MultiBiomeSelector.getElements collects with
  toCollection(ArrayList::new) — the list must stay mutable because
  UnifiedMultiSelector's constructor sorts it in place (Stream.toList()
  would be immutable and throw at runtime).
- S7158: use StringBuilder.isEmpty() in Utils.prettifyBiome.
- S6541: split the REQUIRED_BIOMES branch out of the oversized
  createIslandRequirementButton into createBiomeRequirementButton and
  openBiomeSelector helpers.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NKxodNE4h3TsSHMqDEeC8v

Author: tastybento

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

@@ -930,46 +930,7 @@ private PanelItem createIslandRequirementButton(RequirementButton button) {
             description.add(this.user.getTranslation(Constants.CLICK_TO_CHANGE));
         }
         case REQUIRED_BIOMES -> {
-            if (requirements.getRequiredBiomes().isEmpty()) {
-                description.add(this.user.getTranslation(reference + "none"));
-            } else {
-                description.add(this.user.getTranslation(reference + Constants.TITLE_KEY));
-                requirements.getRequiredBiomes()
-                        .forEach(biomeKey -> description.add(this.user.getTranslation(reference + "list", "[biome]",
-                                Utils.prettifyBiome(biomeKey))));
-            }
-
-            icon = new ItemStack(Material.GRASS_BLOCK);
-            clickHandler = (panel, user, clickType, slot) -> {
-                if (clickType.isRightClick()) {
-                    // Right click clears the biome list.
-                    requirements.getRequiredBiomes().clear();
-                    this.build();
-                } else {
-                    // Left click opens the selector, hiding already-chosen biomes.
-                    Set<Biome> excluded = requirements.getRequiredBiomes().stream()
-                            .map(key -> Registry.BIOME.get(NamespacedKey.fromString(key)))
-                            .filter(Objects::nonNull).collect(Collectors.toSet());
-
-                    MultiBiomeSelector.open(this.user, excluded, (status, biomes) -> {
-                        if (Boolean.TRUE.equals(status) && biomes != null) {
-                            biomes.forEach(biome -> requirements.getRequiredBiomes()
-                                    .add(MultiBiomeSelector.biomeKey(biome)));
-                        }
-
-                        this.build();
-                    });
-                }
-                return true;
-            };
-            glow = false;
-
-            description.add("");
-            description.add(this.user.getTranslation(Constants.TIPS + "click-to-add"));
-
-            if (!requirements.getRequiredBiomes().isEmpty()) {
-                description.add(this.user.getTranslation(Constants.TIPS + "right-click-to-clear"));
-            }
+            return this.createBiomeRequirementButton(requirements, reference, name);
         }
         default -> {
             icon = new ItemStack(Material.PAPER);
@@ -981,6 +942,67 @@ private PanelItem createIslandRequirementButton(RequirementButton button) {
                 .clickHandler(clickHandler).build();
     }
 
+
+    /**
+     * Creates the "Required Biomes" button for island challenges. Left-click opens the biome
+     * selector (hiding already-chosen biomes); right-click clears the list.
+     *
+     * @param requirements the island requirements being edited.
+     * @param reference the translation reference for this button.
+     * @param name the pre-translated button name.
+     * @return the PanelItem for the biome requirement button.
+     */
+    private PanelItem createBiomeRequirementButton(IslandRequirements requirements, String reference, String name) {
+        final List<String> description = new ArrayList<>();
+
+        if (requirements.getRequiredBiomes().isEmpty()) {
+            description.add(this.user.getTranslation(reference + "none"));
+        } else {
+            description.add(this.user.getTranslation(reference + Constants.TITLE_KEY));
+            requirements.getRequiredBiomes().forEach(biomeKey -> description.add(
+                    this.user.getTranslation(reference + "list", "[biome]", Utils.prettifyBiome(biomeKey))));
+        }
+
+        description.add("");
+        description.add(this.user.getTranslation(Constants.CLICK_TO_ADD));
+
+        if (!requirements.getRequiredBiomes().isEmpty()) {
+            description.add(this.user.getTranslation(Constants.TIPS + "right-click-to-clear"));
+        }
+
+        return new PanelItemBuilder().icon(new ItemStack(Material.GRASS_BLOCK)).name(name).description(description)
+                .glow(false).clickHandler((panel, user, clickType, slot) -> {
+                    if (clickType.isRightClick()) {
+                        requirements.getRequiredBiomes().clear();
+                        this.build();
+                    } else {
+                        this.openBiomeSelector(requirements);
+                    }
+                    return true;
+                }).build();
+    }
+
+
+    /**
+     * Opens the biome selector for the given island requirements, excluding already-chosen
+     * biomes, and adds the chosen biomes back to the requirement before rebuilding the panel.
+     *
+     * @param requirements the island requirements being edited.
+     */
+    private void openBiomeSelector(IslandRequirements requirements) {
+        Set<Biome> excluded = requirements.getRequiredBiomes().stream()
+                .map(key -> Registry.BIOME.get(NamespacedKey.fromString(key)))
+                .filter(Objects::nonNull).collect(Collectors.toSet());
+
+        MultiBiomeSelector.open(this.user, excluded, (status, biomes) -> {
+            if (Boolean.TRUE.equals(status) && biomes != null) {
+                biomes.forEach(biome -> requirements.getRequiredBiomes().add(MultiBiomeSelector.biomeKey(biome)));
+            }
+
+            this.build();
+        });
+    }
+
     /**
      * This method creates buttons for inventory requirements menu.
      * 
@@ -1138,7 +1160,7 @@ private PanelItem createInventoryRequirementButton(RequirementButton button) {
             glow = false;
 
             description.add("");
-            description.add(this.user.getTranslation(Constants.TIPS + "click-to-add"));
+            description.add(this.user.getTranslation(Constants.CLICK_TO_ADD));
         }
         case REMOVE_IGNORED_META -> {
             icon = new ItemStack(Material.RED_SHULKER_BOX);
@@ -1843,7 +1865,7 @@ private PanelItem createRewardButton(RewardButton button) {
             glow = false;
 
             description.add("");
-            description.add(this.user.getTranslation(Constants.TIPS + "click-to-add"));
+            description.add(this.user.getTranslation(Constants.CLICK_TO_ADD));
         }
         case REMOVE_IGNORED_META -> {
             icon = new ItemStack(Material.RED_SHULKER_BOX);

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

@@ -1,5 +1,6 @@
 package world.bentobox.challenges.panel.util;
 
+import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Comparator;
 import java.util.HashSet;
@@ -58,10 +59,11 @@ public static void open(User user, BiConsumer<Boolean, Collection<Biome>> consum
 
     @Override
     protected List<Biome> getElements() {
+        // A mutable list is required: UnifiedMultiSelector's constructor sorts it in place.
         return StreamSupport.stream(Registry.BIOME.spliterator(), false)
                 .filter(biome -> excluded == null || !excluded.contains(biome))
                 .sorted(Comparator.comparing(MultiBiomeSelector::biomeKey))
-                .collect(Collectors.toList());
+                .collect(Collectors.toCollection(ArrayList::new));
     }
 
     @Override

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

@@ -249,6 +249,8 @@ public class Constants
 
     public static final String CLICK_TO_CHANGE = TIPS + "click-to-change";
 
+    public static final String CLICK_TO_ADD = TIPS + "click-to-add";
+
     public static final String CLICK_TO_TOGGLE = TIPS + "click-to-toggle";
 
     public static final String CLICK_TO_OPEN = TIPS + "click-to-open";

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

@@ -280,7 +280,7 @@ public static String prettifyBiome(String key)
 				continue;
 			}
 
-			if (builder.length() > 0)
+			if (!builder.isEmpty())
 			{
 				builder.append(' ');
 			}