Paper/paper-server/nms-patches/WorldGenVillagePieces.patch

--- a/net/minecraft/server/WorldGenVillagePieces.java
+++ b/net/minecraft/server/WorldGenVillagePieces.java
@@ -1662,14 +1662,14 @@
                         entityzombievillager.prepare(generatoraccess.getDamageScaler(new BlockPosition(entityzombievillager)), (GroupDataEntity) null, (NBTTagCompound) null);
                         entityzombievillager.setProfession(this.c(i1, 0));
                         entityzombievillager.di();
-                        generatoraccess.addEntity(entityzombievillager);
+                        generatoraccess.addEntity(entityzombievillager, org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason.CHUNK_GEN); // CraftBukkit - add SpawnReason
                     } else {
                         EntityVillager entityvillager = new EntityVillager(generatoraccess.getMinecraftWorld());
 
                         entityvillager.setPositionRotation((double) j1 + 0.5D, (double) k1, (double) l1 + 0.5D, 0.0F, 0.0F);
                         entityvillager.setProfession(this.c(i1, generatoraccess.m().nextInt(6)));
                         entityvillager.a(generatoraccess.getDamageScaler(new BlockPosition(entityvillager)), (GroupDataEntity) null, (NBTTagCompound) null, false);
-                        generatoraccess.addEntity(entityvillager);
+                        generatoraccess.addEntity(entityvillager, org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason.CHUNK_GEN); // CraftBukkit - add SpawnReason
                     }
                 }