The wither boss' loot table is not changed when it's DeathLootTable NBT data is modified, resulting in it always dropping a nether star.

Steps to Reproduce:

1. Summon a wither with no AI

   /summon minecraft:wither ~ ~ ~ {NoAI:1b}
   

2. Modify it's data to be empty

   /data modify entity @e[type=wither,limit=1,sort=nearest] DeathLootTable set value ""
   

3. Kill it

   /kill @e[type=wither]
   

Expected & Observed Results:

- The wither will drop a nether star, despite having no DeathLootTable NBT data
- It would not drop anything, as that is what the player intentionally set the DeathLootTable to.


Screenshots/Videos:

 WitherBossDeathLootTable.mp4

Code Analysis

The happens because the wither boss has it's death loot table "hard-coded", meaning it ignores any loot table entirely.

Class: net.minecraft.world.entity.boss.wither.WitherBoss // Method: dropCustomDeathLoot // MCP 1.20.2 Mojang Mappings

   protected void dropCustomDeathLoot(DamageSource source, int lootingMultiplier, boolean allowDrops) {
      super.dropCustomDeathLoot(source, lootingMultiplier, allowDrops);
      ItemEntity itementity = this.spawnAtLocation(Items.NETHER_STAR);
      if (itementity != null) {
         itementity.setExtendedLifetime();
      }
   }

Original Description:

The bug

Setting the wither's DeathLootTable NBT tag to any given loot table does not stop the wither from dropping a nether star.
Loot from the loot table set in the DeathLootTable tag drops in addition to the nether star. This was not the case in 1.13.*, where the DeathLootTable tag being set prevented the nether star from dropping.