--- a/net/minecraft/util/worldupdate/WorldUpgrader.java
+++ b/net/minecraft/util/worldupdate/WorldUpgrader.java
@@ -81,7 +81,7 @@
 
     public WorldUpgrader(Convertable.ConversionSession convertable_conversionsession, DataFixer datafixer, IRegistryCustom iregistrycustom, boolean flag, boolean flag1) {
         this.dimensions = iregistrycustom.registryOrThrow(Registries.LEVEL_STEM);
-        this.levels = (Set) this.dimensions.registryKeySet().stream().map(Registries::levelStemToLevel).collect(Collectors.toUnmodifiableSet());
+        this.levels = (Set) java.util.stream.Stream.of(convertable_conversionsession.dimensionType).map(Registries::levelStemToLevel).collect(Collectors.toUnmodifiableSet()); // CraftBukkit
         this.eraseCache = flag;
         this.dataFixer = datafixer;
         this.levelStorage = convertable_conversionsession;
@@ -194,9 +194,9 @@
             if (nbttagcompound != null) {
                 int i = IChunkLoader.getVersion(nbttagcompound);
                 ChunkGenerator chunkgenerator = ((WorldDimension) WorldUpgrader.this.dimensions.getOrThrow(Registries.levelToLevelStem(resourcekey))).generator();
-                NBTTagCompound nbttagcompound1 = ichunkloader.upgradeChunkTag(resourcekey, () -> {
+                NBTTagCompound nbttagcompound1 = ichunkloader.upgradeChunkTag(Registries.levelToLevelStem(resourcekey), () -> { // CraftBukkit
                     return WorldUpgrader.this.overworldDataStorage;
-                }, nbttagcompound, chunkgenerator.getTypeNameForDataFixer());
+                }, nbttagcompound, chunkgenerator.getTypeNameForDataFixer(), chunkcoordintpair, null); // CraftBukkit
                 ChunkCoordIntPair chunkcoordintpair1 = new ChunkCoordIntPair(nbttagcompound1.getInt("xPos"), nbttagcompound1.getInt("zPos"));
 
                 if (!chunkcoordintpair1.equals(chunkcoordintpair)) {
@@ -316,7 +316,7 @@
                         WorldUpgrader.c<T> worldupgrader_c = (WorldUpgrader.c) iterator.next();
                         ResourceKey<World> resourcekey = worldupgrader_c.dimensionKey;
                         ListIterator<WorldUpgrader.e> listiterator = worldupgrader_c.files;
-                        T t0 = (AutoCloseable) worldupgrader_c.storage;
+                        T t0 = (T) worldupgrader_c.storage; // CraftBukkit - decompile error
 
                         if (listiterator.hasNext()) {
                             WorldUpgrader.e worldupgrader_e = (WorldUpgrader.e) listiterator.next();