Partially fix #6880 (#6888)

patches/server/0826-Use-correct-LevelStem-registry-when-loading-default-.patch

@@ -6,17 +6,19 @@ Subject: [PATCH] Use correct LevelStem registry when loading default
 
 
 diff --git a/src/main/java/net/minecraft/server/MinecraftServer.java b/src/main/java/net/minecraft/server/MinecraftServer.java
-index c8876b000a03f18e7a140167ed4505a9843a8d14..7636b0ae9031e06fd8b4a0c359a45a17e6e075de 100644
+index 57cb2722e973cfc8edc845bc7154b8b8bbb11e12..5a4172faaf960d48939d6a485719041987df9242 100644
 --- a/src/main/java/net/minecraft/server/MinecraftServer.java
 +++ b/src/main/java/net/minecraft/server/MinecraftServer.java
-@@ -641,7 +641,12 @@ public abstract class MinecraftServer extends ReentrantBlockableEventLoop<TickTa
+@@ -641,7 +641,14 @@ 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) {
++            final LevelStem worlddimension;
++            if (dimensionKey == LevelStem.END || dimensionKey == LevelStem.NETHER) {
++                worlddimension = generatorsettings.dimensions().get(dimensionKey);
++            } else {
 +                worlddimension = registrymaterials.get(dimensionKey);
 +            }
 +            // Paper end