[TML 1.4.4] Make NPCs drop tombstones on death.

[MGTro (Dice)]

Hello. I've been trying to make a new mod lately, but I don't understand how the new IEntitySource works.. I want to experiment by making town npcs drop tombstones on death, just like players do. But I come across this:

Item.NewItem(npc.GetSource_Death(), tombstone);

It wont let me go further because I don't have an IEntitySource thing added. Here's the full class:

using Terraria;
using Terraria.ID;
using Terraria.ModLoader;

namespace npcTombstones
{
    public class TombstoneNPC : GlobalNPC
    {
        public override void OnKill(NPC npc)
        {
            if (!npc.townNPC)
            {
                return;
            }
            Item tombstone = new Item();
            tombstone.SetDefaults(ItemID.Tombstone);
            tombstone.position = npc.position;


            Item.NewItem(npc.GetSource_Death(), tombstone);


        }
    }
}