Program: 10229
Project: 10229
Buggy source:
@EventHandler(priority=EventPriority.MONITOR,ignoreCancelled=true) public void onDamage(EntityDamageEvent event){
  if (event.getEntity() != npc.getBukkitEntity() || dying)   return;
  if (this.getHealth() - event.getDamage() > 0)   return;
  dying=true;
  player=null;
  entityId=npc.getBukkitEntity().getEntityId();
  String deathCause=event.getCause().toString().toLowerCase().replace('_',' ');
  Map<String,dObject> context=new HashMap<String,dObject>();
  context.put("String_Node_Str",new Element(event.getDamage()));
  context.put("String_Node_Str",new Element(deathCause));
  if (event instanceof EntityDamageByEntityEvent) {
    Entity killerEntity=((EntityDamageByEntityEvent)event).getDamager();
    context.put("String_Node_Str",new dEntity(killerEntity));
    if (killerEntity instanceof Player)     player=dPlayer.mirrorBukkitPlayer((Player)killerEntity);
 else     if (killerEntity instanceof Projectile) {
      ProjectileSource shooter=((Projectile)killerEntity).getShooter();
      if (shooter != null && shooter instanceof LivingEntity) {
        context.put("String_Node_Str",new dEntity((LivingEntity)shooter));
        if (shooter instanceof Player)         player=dPlayer.mirrorBukkitPlayer((Player)shooter);
        DenizenAPI.getDenizenNPC(npc).action("String_Node_Str" + ((LivingEntity)shooter).getType().toString(),player,context);
      }
    }
    DenizenAPI.getDenizenNPC(npc).action("String_Node_Str",player,context);
    DenizenAPI.getDenizenNPC(npc).action("String_Node_Str" + killerEntity.getType().toString(),player,context);
  }
 else   if (event instanceof EntityDamageByBlockEvent) {
    DenizenAPI.getDenizenNPC(npc).action("String_Node_Str",player,context);
  }
  DenizenAPI.getDenizenNPC(npc).action("String_Node_Str",player,context);
  DenizenAPI.getDenizenNPC(npc).action("String_Node_Str" + deathCause,player,context);
  if (npc.getBukkitEntity() == null)   return;
  loc=dLocation.valueOf(TagManager.tag(null,DenizenAPI.getDenizenNPC(npc),respawnLocation,false));
  if (loc == null)   loc=npc.getBukkitEntity().getLocation();
  if (animatedeath) {
    npc.getNavigator().cancelNavigation();
  }
  die();
  if (respawn) {
    Bukkit.getServer().getScheduler().scheduleSyncDelayedTask(DenizenAPI.getCurrentInstance(),new Runnable(){
      public void run(){
        if (CitizensAPI.getNPCRegistry().getById(npc.getId()) == null || npc.isSpawned())         return;
 else         npc.spawn(loc);
      }
    }
,(Duration.valueOf(respawnDelay).getTicks()));
  }
}

Fixed version (ground truth):
@EventHandler(priority=EventPriority.MONITOR,ignoreCancelled=true) public void onDamage(EntityDamageEvent event){
  if (event.getEntity() != npc.getBukkitEntity() || dying)   return;
  if (this.getHealth() - event.getDamage() > 0)   return;
  dying=true;
  player=null;
  entityId=npc.getBukkitEntity().getEntityId();
  String deathCause=event.getCause().toString().toLowerCase().replace('_',' ');
  Map<String,dObject> context=new HashMap<String,dObject>();
  context.put("String_Node_Str",new Element(event.getDamage()));
  context.put("String_Node_Str",new Element(deathCause));
  if (event instanceof EntityDamageByEntityEvent) {
    Entity killerEntity=((EntityDamageByEntityEvent)event).getDamager();
    context.put("String_Node_Str",new dEntity(killerEntity));
    if (killerEntity instanceof Player)     player=dPlayer.mirrorBukkitPlayer((Player)killerEntity);
 else     if (killerEntity instanceof Projectile) {
      ProjectileSource shooter=((Projectile)killerEntity).getShooter();
      if (shooter != null && shooter instanceof LivingEntity) {
        context.put("String_Node_Str",new dEntity((LivingEntity)shooter));
        if (shooter instanceof Player)         player=dPlayer.mirrorBukkitPlayer((Player)shooter);
        DenizenAPI.getDenizenNPC(npc).action("String_Node_Str" + ((LivingEntity)shooter).getType().toString(),player,context);
      }
    }
    DenizenAPI.getDenizenNPC(npc).action("String_Node_Str",player,context);
    DenizenAPI.getDenizenNPC(npc).action("String_Node_Str" + killerEntity.getType().toString(),player,context);
  }
 else   if (event instanceof EntityDamageByBlockEvent) {
    DenizenAPI.getDenizenNPC(npc).action("String_Node_Str",player,context);
  }
  DenizenAPI.getDenizenNPC(npc).action("String_Node_Str",player,context);
  DenizenAPI.getDenizenNPC(npc).action("String_Node_Str" + deathCause,player,context);
  if (npc.getBukkitEntity() == null)   return;
  loc=dLocation.valueOf(TagManager.tag(null,DenizenAPI.getDenizenNPC(npc),respawnLocation,false));
  if (loc == null)   loc=npc.getBukkitEntity().getLocation();
  if (animatedeath) {
    npc.getNavigator().cancelNavigation();
  }
  die();
  if (respawn && (Duration.valueOf(respawnDelay).getTicks() > 0)) {
    Bukkit.getServer().getScheduler().scheduleSyncDelayedTask(DenizenAPI.getCurrentInstance(),new Runnable(){
      public void run(){
        if (CitizensAPI.getNPCRegistry().getById(npc.getId()) == null || npc.isSpawned())         return;
 else         npc.spawn(loc);
      }
    }
,(Duration.valueOf(respawnDelay).getTicks()));
  }
}