Fix misaligned patch causing monsters to not spawn in nether fortresses correctly.

src/main/java/net/minecraftforge/common/extensions/IForgeStructureFeature.java

@@ -33,10 +33,28 @@ public interface IForgeStructureFeature
         return (StructureFeature<?>) this;
     }
 
+    /**
+     * Gets the default list of spawns for this structure, of the specified category.
+     *
+     * @apiNote Implement this over any of the type specific getSpecial functions in StructureFeature.
+     */
+    @SuppressWarnings("incomplete-switch")
+    default List<MobSpawnSettings.SpawnerData> getDefaultSpawnList(MobCategory category)
+    {
+        if (category == MobCategory.MONSTER)
+            return getDefaultSpawnList();
+        else if (category == MobCategory.CREATURE)
+            return getDefaultCreatureSpawnList();
+        return Collections.emptyList();
+    }
+
     /**
      * Gets the default list of {@link EntityClassification#MONSTER} spawns for this structure.
      *
      * @apiNote Implement this over {@link Structure#getSpawnList()}
+     *
+     * @Deprecated Use {@link IForgeStructureFeature#getDefaultSpawnList(MobCategory)}
+     * TODO: Remove in 1.18
      */
     default List<MobSpawnSettings.SpawnerData> getDefaultSpawnList()
     {
@@ -47,6 +65,9 @@ public interface IForgeStructureFeature
      * Gets the default list of {@link EntityClassification#CREATURE} spawns for this structure.
      *
      * @apiNote Implement this over {@link Structure#getCreatureSpawnList()}
+     *
+     * @Deprecated Use {@link IForgeStructureFeature#getDefaultSpawnList(MobCategory)}
+     * TODO: Remove in 1.18
      */
     default List<MobSpawnSettings.SpawnerData> getDefaultCreatureSpawnList()
     {

src/main/java/net/minecraftforge/common/world/StructureSpawnManager.java

@@ -111,8 +111,9 @@ public class StructureSpawnManager
      */
     public static WeightedRandomList<MobSpawnSettings.SpawnerData> getSpawnList(StructureFeature<?> structure, MobCategory classification)
     {
-        if (structuresWithSpawns.containsKey(structure))
-            return structuresWithSpawns.get(structure).spawns.getOrDefault(classification, WeightedRandomList.create());
+        StructureSpawnInfo info = structuresWithSpawns.get(structure);
+        if (info != null)
+            return info.spawns.getOrDefault(classification, WeightedRandomList.create());
         return WeightedRandomList.create();
     }
 

src/main/java/net/minecraftforge/event/world/StructureSpawnListGatherEvent.java

@@ -25,7 +25,9 @@ import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import net.minecraft.world.entity.MobCategory;
+import net.minecraft.world.level.SpawnData;
 import net.minecraft.world.level.biome.MobSpawnSettings;
+import net.minecraft.world.level.biome.MobSpawnSettings.SpawnerData;
 import net.minecraft.world.level.levelgen.feature.StructureFeature;
 import net.minecraftforge.eventbus.api.Event;
 
@@ -55,8 +57,12 @@ public class StructureSpawnListGatherEvent extends Event
     {
         this.structure = structure;
         this.insideOnly = this.structure.getDefaultRestrictsSpawnsToInside();
-        addEntitySpawns(MobCategory.MONSTER, this.structure.getDefaultSpawnList());
-        addEntitySpawns(MobCategory.CREATURE, this.structure.getDefaultCreatureSpawnList());
+
+        for (MobCategory cat : MobCategory.values()) {
+            List<SpawnerData> lst = this.structure.getDefaultSpawnList(cat);
+            if (!lst.isEmpty())
+                addEntitySpawns(cat, lst);
+        }
     }
 
     /**