Program: 93771
Project: 93771
Buggy source:
private String getMessage(final EntityDamageEvent e){
  final Entity damager=((EntityDamageByEntityEvent)e).getDamager();
  if (damager instanceof Wolf) {
    return ACHelper.getInstance().getDeathMessage("String_Node_Str");
  }
 else   if (damager instanceof Skeleton) {
    return ACHelper.getInstance().getDeathMessage("String_Node_Str");
  }
 else   if (damager instanceof TNTPrimed) {
    return ACHelper.getInstance().getDeathMessage("String_Node_Str");
  }
 else   if (damager instanceof Zombie) {
    return ACHelper.getInstance().getDeathMessage("String_Node_Str");
  }
 else   if (damager instanceof Projectile) {
    if (damager instanceof Arrow) {
      if (((Arrow)damager).getShooter() == null) {
        return ACHelper.getInstance().getDeathMessage("String_Node_Str");
      }
 else       if (((Arrow)damager).getShooter() instanceof Player) {
        return ACHelper.getInstance().getDeathMessage("String_Node_Str") + Utils.getPlayerName(((Player)((Arrow)damager).getShooter()));
      }
 else       if (((Projectile)damager).getShooter() instanceof Skeleton) {
        return ACHelper.getInstance().getDeathMessage("String_Node_Str");
      }
    }
 else     if (damager instanceof Fireball) {
      if (((Fireball)damager).getShooter() instanceof Blaze) {
        return ACHelper.getInstance().getDeathMessage("String_Node_Str");
      }
 else       if (((Fireball)damager).getShooter() instanceof Ghast) {
        return ACHelper.getInstance().getDeathMessage("String_Node_Str");
      }
    }
 else     if (damager instanceof ThrownPotion) {
      if (((ThrownPotion)damager).getShooter() instanceof Player) {
        return ACHelper.getInstance().getDeathMessage("String_Node_Str");
      }
    }
  }
 else   if (damager instanceof LivingEntity) {
    return ACHelper.getInstance().getDeathMessage("String_Node_Str") + damager.getType().getName();
  }
  return ACHelper.getInstance().getDeathMessage("String_Node_Str");
}

Fixed version (ground truth):
private String getMessage(final EntityDamageEvent e){
  final Entity damager=((EntityDamageByEntityEvent)e).getDamager();
  if (damager instanceof Wolf) {
    return ACHelper.getInstance().getDeathMessage("String_Node_Str");
  }
 else   if (damager instanceof Player) {
    return ACHelper.getInstance().getDeathMessage("String_Node_Str");
  }
 else   if (damager instanceof Skeleton) {
    return ACHelper.getInstance().getDeathMessage("String_Node_Str");
  }
 else   if (damager instanceof TNTPrimed) {
    return ACHelper.getInstance().getDeathMessage("String_Node_Str");
  }
 else   if (damager instanceof Zombie) {
    if (damager instanceof PigZombie) {
      return ACHelper.getInstance().getDeathMessage("String_Node_Str");
    }
    return ACHelper.getInstance().getDeathMessage("String_Node_Str");
  }
 else   if (damager instanceof Projectile) {
    if (damager instanceof Arrow) {
      if (((Arrow)damager).getShooter() == null) {
        return ACHelper.getInstance().getDeathMessage("String_Node_Str");
      }
 else       if (((Arrow)damager).getShooter() instanceof Player) {
        return ACHelper.getInstance().getDeathMessage("String_Node_Str") + Utils.getPlayerName(((Player)((Arrow)damager).getShooter()));
      }
 else       if (((Projectile)damager).getShooter() instanceof Skeleton) {
        return ACHelper.getInstance().getDeathMessage("String_Node_Str");
      }
    }
 else     if (damager instanceof Fireball) {
      if (((Fireball)damager).getShooter() instanceof Blaze) {
        return ACHelper.getInstance().getDeathMessage("String_Node_Str");
      }
 else       if (((Fireball)damager).getShooter() instanceof Ghast) {
        return ACHelper.getInstance().getDeathMessage("String_Node_Str");
      }
    }
 else     if (damager instanceof ThrownPotion) {
      if (((ThrownPotion)damager).getShooter() instanceof Player) {
        return ACHelper.getInstance().getDeathMessage("String_Node_Str");
      }
    }
  }
 else   if (damager instanceof LivingEntity) {
    return (ACHelper.getInstance().getDeathMessage("String_Node_Str") + damager.getType().getName());
  }
  return ACHelper.getInstance().getDeathMessage("String_Node_Str");
}