Paper/nms-patches/WorldGenRegistration.patch

--- a/net/minecraft/server/WorldGenRegistration.java
+++ b/net/minecraft/server/WorldGenRegistration.java
@@ -108,7 +108,7 @@
 
                         entitywitch.setPositionRotation((double) i1 + 0.5D, (double) j1, (double) k1 + 0.5D, 0.0F, 0.0F);
                         entitywitch.prepare(world.E(new BlockPosition(i1, j1, k1)), (GroupDataEntity) null);
-                        world.addEntity(entitywitch);
+                        world.addEntity(entitywitch, org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason.CHUNK_GEN); // CraftBukkit - add SpawnReason
                     }
                 }