Use correct LevelStem registry when loading default end/nether (#6789)

patches/server/Use-correct-LevelStem-registry-when-loading-default-.patch

@@ -0,0 +1,25 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Jason Penilla <11360596+jpenilla@users.noreply.github.com>
+Date: Sat, 16 Oct 2021 17:38:35 -0700
+Subject: [PATCH] Use correct LevelStem registry when loading default
+ end/nether
+
+
+diff --git a/src/main/java/net/minecraft/server/MinecraftServer.java b/src/main/java/net/minecraft/server/MinecraftServer.java
+index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
+--- a/src/main/java/net/minecraft/server/MinecraftServer.java
++++ b/src/main/java/net/minecraft/server/MinecraftServer.java
+@@ -0,0 +0,0 @@ public abstract class MinecraftServer extends ReentrantBlockableEventLoop<TickTa
+             long i = generatorsettings.seed();
+             long j = BiomeManager.obfuscateSeed(i);
+             List<CustomSpawner> list = ImmutableList.of(new PhantomSpawner(), new PatrolSpawner(), new CatSpawner(), new VillageSiege(), new WanderingTraderSpawner(iworlddataserver));
+-            LevelStem worlddimension = (LevelStem) registrymaterials.get(dimensionKey);
++            // Paper start - Use correct LevelStem registry
++            LevelStem worlddimension = generatorsettings.dimensions().get(dimensionKey);
++            if (worlddimension == null) {
++                worlddimension = registrymaterials.get(dimensionKey);
++            }
++            // Paper end
+             DimensionType dimensionmanager;
+             ChunkGenerator chunkgenerator;
+