Use WeakReference in ServerWorldPropertiesRegistry

src/main/java/com/moulberry/axiom/AxiomPaper.java

@@ -42,6 +42,7 @@ import org.incendo.cloud.paper.LegacyPaperCommandManager;
 import org.jetbrains.annotations.Nullable;
 
 import java.io.IOException;
+import java.lang.ref.WeakReference;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.*;
@@ -401,7 +402,7 @@ public class AxiomPaper extends JavaPlugin implements Listener {
     }
 
     private ServerWorldPropertiesRegistry createWorldProperties(World world) {
-        ServerWorldPropertiesRegistry registry = new ServerWorldPropertiesRegistry(world);
+        ServerWorldPropertiesRegistry registry = new ServerWorldPropertiesRegistry(new WeakReference<>(world));
 
         AxiomCreateWorldPropertiesEvent createEvent = new AxiomCreateWorldPropertiesEvent(world, registry);
         Bukkit.getPluginManager().callEvent(createEvent);

src/main/java/com/moulberry/axiom/world_properties/server/ServerWorldPropertiesRegistry.java

@@ -13,15 +13,16 @@ import org.bukkit.craftbukkit.v1_20_R2.CraftWorld;
 import org.bukkit.entity.Player;
 import org.bukkit.plugin.Plugin;
 
+import java.lang.ref.Reference;
 import java.util.*;
 
 public class ServerWorldPropertiesRegistry {
 
     private final LinkedHashMap<WorldPropertyCategory, List<ServerWorldPropertyHolder<?>>> propertyList = new LinkedHashMap<>();
     private final Map<ResourceLocation, ServerWorldPropertyHolder<?>> propertyMap = new HashMap<>();
-    private final World world;
+    private final Reference<World> world;
 
-    public ServerWorldPropertiesRegistry(World world) {
+    public ServerWorldPropertiesRegistry(Reference<World> world) {
         this.world = world;
         this.registerDefault();
     }
@@ -32,9 +33,14 @@ public class ServerWorldPropertiesRegistry {
 
     @SuppressWarnings("unchecked")
     public void addCategory(WorldPropertyCategory category, List<ServerWorldPropertyBase<?>> properties) {
+        World world = this.world.get();
+        if (world == null) {
+            return;
+        }
+
         List<ServerWorldPropertyHolder<?>> holders = new ArrayList<>();
         for (ServerWorldPropertyBase<?> property : properties) {
-            Object defaultValue = property.getDefaultValue(this.world);
+            Object defaultValue = property.getDefaultValue(world);
             holders.add(new ServerWorldPropertyHolder<>(defaultValue, (ServerWorldPropertyBase<Object>) property));
         }