--- a/net/minecraft/server/WorldUpgrader.java
+++ b/net/minecraft/server/WorldUpgrader.java
@@ -25,7 +25,7 @@
 
     private static final Logger LOGGER = LogManager.getLogger();
     private static final ThreadFactory b = (new ThreadFactoryBuilder()).setDaemon(true).build();
-    private final ImmutableSet<ResourceKey<World>> c;
+    private final ImmutableSet<ResourceKey<DimensionManager>> c; // CraftBukkit
     private final boolean d;
     private final Convertable.ConversionSession e;
     private final Thread f;
@@ -36,12 +36,12 @@
     private volatile int k;
     private volatile int l;
     private volatile int m;
-    private final Object2FloatMap<ResourceKey<World>> n = Object2FloatMaps.synchronize(new Object2FloatOpenCustomHashMap(SystemUtils.k()));
+    private final Object2FloatMap<ResourceKey<DimensionManager>> n = Object2FloatMaps.synchronize(new Object2FloatOpenCustomHashMap(SystemUtils.k())); // CraftBukkit
     private volatile IChatBaseComponent o = new ChatMessage("optimizeWorld.stage.counting");
     private static final Pattern p = Pattern.compile("^r\\.(-?[0-9]+)\\.(-?[0-9]+)\\.mca$");
     private final WorldPersistentData q;
 
-    public WorldUpgrader(Convertable.ConversionSession convertable_conversionsession, DataFixer datafixer, ImmutableSet<ResourceKey<World>> immutableset, boolean flag) {
+    public WorldUpgrader(Convertable.ConversionSession convertable_conversionsession, DataFixer datafixer, ImmutableSet<ResourceKey<DimensionManager>> immutableset, boolean flag) { // CraftBukkit
         this.c = immutableset;
         this.d = flag;
         this.g = datafixer;
@@ -69,12 +69,12 @@
 
     private void i() {
         this.k = 0;
-        Builder<ResourceKey<World>, ListIterator<ChunkCoordIntPair>> builder = ImmutableMap.builder();
+        Builder<ResourceKey<DimensionManager>, ListIterator<ChunkCoordIntPair>> builder = ImmutableMap.builder(); // CraftBukkit
 
         List list;
 
         for (UnmodifiableIterator unmodifiableiterator = this.c.iterator(); unmodifiableiterator.hasNext(); this.k += list.size()) {
-            ResourceKey<World> resourcekey = (ResourceKey) unmodifiableiterator.next();
+            ResourceKey<DimensionManager> resourcekey = (ResourceKey) unmodifiableiterator.next(); // CraftBukkit
 
             list = this.b(resourcekey);
             builder.put(resourcekey, list.listIterator());
@@ -84,18 +84,18 @@
             this.i = true;
         } else {
             float f = (float) this.k;
-            ImmutableMap<ResourceKey<World>, ListIterator<ChunkCoordIntPair>> immutablemap = builder.build();
-            Builder<ResourceKey<World>, IChunkLoader> builder1 = ImmutableMap.builder();
+            ImmutableMap<ResourceKey<DimensionManager>, ListIterator<ChunkCoordIntPair>> immutablemap = builder.build(); // CraftBukkit
+            Builder<ResourceKey<DimensionManager>, IChunkLoader> builder1 = ImmutableMap.builder(); // CraftBukkit
             UnmodifiableIterator unmodifiableiterator1 = this.c.iterator();
 
             while (unmodifiableiterator1.hasNext()) {
-                ResourceKey<World> resourcekey1 = (ResourceKey) unmodifiableiterator1.next();
-                File file = this.e.a(resourcekey1);
+                ResourceKey<DimensionManager> resourcekey1 = (ResourceKey) unmodifiableiterator1.next(); // CraftBukkit
+                File file = this.e.a(null); // CraftBukkit
 
                 builder1.put(resourcekey1, new IChunkLoader(new File(file, "region"), this.g, true));
             }
 
-            ImmutableMap<ResourceKey<World>, IChunkLoader> immutablemap1 = builder1.build();
+            ImmutableMap<ResourceKey<DimensionManager>, IChunkLoader> immutablemap1 = builder1.build(); // CraftBukkit
             long i = SystemUtils.getMonotonicMillis();
 
             this.o = new ChatMessage("optimizeWorld.stage.upgrading");
@@ -107,7 +107,7 @@
                 float f2;
 
                 for (UnmodifiableIterator unmodifiableiterator2 = this.c.iterator(); unmodifiableiterator2.hasNext(); f1 += f2) {
-                    ResourceKey<World> resourcekey2 = (ResourceKey) unmodifiableiterator2.next();
+                    ResourceKey<DimensionManager> resourcekey2 = (ResourceKey) unmodifiableiterator2.next(); // CraftBukkit
                     ListIterator<ChunkCoordIntPair> listiterator = (ListIterator) immutablemap.get(resourcekey2);
                     IChunkLoader ichunkloader = (IChunkLoader) immutablemap1.get(resourcekey2);
 
@@ -122,7 +122,7 @@
                                 int j = IChunkLoader.a(nbttagcompound);
                                 NBTTagCompound nbttagcompound1 = ichunkloader.getChunkData(resourcekey2, () -> {
                                     return this.q;
-                                }, nbttagcompound);
+                                }, nbttagcompound, chunkcoordintpair, null); // CraftBukkit
                                 NBTTagCompound nbttagcompound2 = nbttagcompound1.getCompound("Level");
                                 ChunkCoordIntPair chunkcoordintpair1 = new ChunkCoordIntPair(nbttagcompound2.getInt("xPos"), nbttagcompound2.getInt("zPos"));
 
@@ -195,8 +195,8 @@
         }
     }
 
-    private List<ChunkCoordIntPair> b(ResourceKey<World> resourcekey) {
-        File file = this.e.a(resourcekey);
+    private List<ChunkCoordIntPair> b(ResourceKey<DimensionManager> resourcekey) { // CraftBukkit
+        File file = this.e.a(null); // CraftBukkit
         File file1 = new File(file, "region");
         File[] afile = file1.listFiles((file2, s) -> {
             return s.endsWith(".mca");