Shapeless recipes accept anything in empty tag ingredients. (As long as there is something).

For example, the following recipe:

{
  "type": "minecraft:crafting_shapeless",
  "category": "building",
  "ingredients": [
    "minecraft:diorite",
    "#c:cobblestones/doesntexist"
  ],
  "result": {
    "count": 2,
    "id": "minecraft:diamond"
  }
}

with the following tag file for the tag:

{
  "values": []
}

causes a warning to be printed in the chat:

Recipe minecraft:test_recipe can't be placed due to empty ingredients and will be ignored

However, the recipe will accept any two items and give two diamonds as a result.

How to reproduce:

The attached data pack contains a shapeless recipe that accepts stone and an empty tag and returns smooth stone, and an empty item tag.

1. Add the attached data pack to a world.
2. Place any two items in a crafting grid.
   → Smooth stone appears in the crafting output.

Expected result:

The recipe wouldn't validate due to the empty tag in the ingredients list.

Observed result:

A message is printed in the log saying that the recipe didn't validate, but putting any two items in a crafting grid outputs smooth stone.

Possible cause:

Looks like the PlacementInfo for the recipe is `PlacementInfo.NOT_PLACEABLE`, but that doesn't prevent the shapeless recipe from matching as long as the item count is equal to the ingredient count.