PaperMC/nms-patches/MobSpawnerAbstract.patch

--- a/net/minecraft/server/MobSpawnerAbstract.java
+++ b/net/minecraft/server/MobSpawnerAbstract.java
@@ -4,6 +4,8 @@
 import java.util.Iterator;
 import java.util.List;
 
+import org.bukkit.event.entity.CreatureSpawnEvent; // CraftBukkit
+
 public abstract class MobSpawnerAbstract {
 
     public int spawnDelay = 20;
@@ -24,6 +26,11 @@
 
     public String getMobName() {
         if (this.i() == null) {
+            // CraftBukkit start - fix NPE
+            if (this.mobName == null) {
+                this.mobName = "Pig";
+            }
+            // CraftBukkit end
             if (this.mobName != null && this.mobName.equals("Minecart")) {
                 this.mobName = "MinecartRideable";
             }
@@ -129,7 +136,7 @@
 
             entity.f(nbttagcompound);
             if (entity.world != null && flag) {
-                entity.world.addEntity(entity);
+                entity.world.addEntity(entity, CreatureSpawnEvent.SpawnReason.SPAWNER); // CraftBukkit
             }
 
             NBTTagCompound nbttagcompound1;
@@ -154,7 +161,7 @@
                     entity2.f(nbttagcompound2);
                     entity2.setPositionRotation(entity1.locX, entity1.locY, entity1.locZ, entity1.yaw, entity1.pitch);
                     if (entity.world != null && flag) {
-                        entity.world.addEntity(entity2);
+                        entity.world.addEntity(entity2, CreatureSpawnEvent.SpawnReason.SPAWNER); // CraftBukkit
                     }
 
                     entity1.mount(entity2);
@@ -167,7 +174,7 @@
                 ((EntityInsentient) entity).prepare(entity.world.E(new BlockPosition(entity)), (GroupDataEntity) null);
             }
 
-            entity.world.addEntity(entity);
+            entity.world.addEntity(entity, CreatureSpawnEvent.SpawnReason.SPAWNER); // CraftBukkit
         }
 
         return entity;