chore: enforce and document notnull chunk loader, add noop impl

src/main/java/net/minestom/server/instance/IChunkLoader.java

@@ -19,6 +19,10 @@ import java.util.concurrent.atomic.AtomicInteger;
  */
 public interface IChunkLoader {
 
+    static @NotNull IChunkLoader noop() {
+        return NoopChunkLoaderImpl.INSTANCE;
+    }
+
     /**
      * Loads instance data from the loader.
      *

src/main/java/net/minestom/server/instance/InstanceContainer.java

@@ -269,9 +269,7 @@ public class InstanceContainer extends Instance {
         // Clear cache
         this.chunks.remove(getChunkIndex(chunkX, chunkZ));
         chunk.unload();
-        if (chunkLoader != null) {
+        chunkLoader.unloadChunk(chunk);
-            chunkLoader.unloadChunk(chunk);
-        }
         var dispatcher = MinecraftServer.process().dispatcher();
         dispatcher.deletePartition(chunk);
     }
@@ -588,17 +586,19 @@ public class InstanceContainer extends Instance {
      *
      * @return the {@link IChunkLoader} of this instance
      */
-    public IChunkLoader getChunkLoader() {
+    public @NotNull IChunkLoader getChunkLoader() {
         return chunkLoader;
     }
 
     /**
      * Changes the {@link IChunkLoader} of this instance (to change how chunks are retrieved when not already loaded).
      *
+     * <p>{@link IChunkLoader#noop()} can be used to do nothing.</p>
+     *
      * @param chunkLoader the new {@link IChunkLoader}
      */
-    public void setChunkLoader(IChunkLoader chunkLoader) {
+    public void setChunkLoader(@NotNull IChunkLoader chunkLoader) {
-        this.chunkLoader = chunkLoader;
+        this.chunkLoader = Objects.requireNonNull(chunkLoader, "Chunk loader cannot be null");
     }
 
     @Override

src/main/java/net/minestom/server/instance/NoopChunkLoaderImpl.java

@@ -0,0 +1,23 @@
+package net.minestom.server.instance;
+
+import net.minestom.server.utils.async.AsyncUtils;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.concurrent.CompletableFuture;
+
+final class NoopChunkLoaderImpl implements IChunkLoader {
+    static final NoopChunkLoaderImpl INSTANCE = new NoopChunkLoaderImpl();
+
+    private NoopChunkLoaderImpl(){}
+
+    @Override
+    public @NotNull CompletableFuture<@Nullable Chunk> loadChunk(@NotNull Instance instance, int chunkX, int chunkZ) {
+        return CompletableFuture.completedFuture(null);
+    }
+
+    @Override
+    public @NotNull CompletableFuture<Void> saveChunk(@NotNull Chunk chunk) {
+        return AsyncUtils.VOID_FUTURE;
+    }
+}