Step to reproduce:

1. Download add-on below and activate into world (All Experimental Features Activated)
2. Using this command to test block /give @s issuetest:transform_item_test
3. Place that's block and interact with an item on it

If using transform_item, all stack of that's item holding will be converted to item in transform_item

"transform_item": {
  "transform": "lava_bucket"
}

Results Received:
Before Event Run | After Event Run
Empty Bucket * 16 -> Lava Bucket * 1

Expected Result:
Before Event Run | After Event Run
Empty Bucket * 16 -> Lava Bucket * 1 And Empty Bucket * 15

Suggest Syntax:

"transform_item": {
  "transforms": [
    {
      "name": "lava_bucket",
      "data": 0,
      "count": 1
    },
    {
      "name": "custom_item",
      "count": 1
    },
    {
      "name": "custom_block",
      "states": [
        "ns:ex": false
      ],
      "count": 64
    },
    ...
  ]
}

Update 1.19.20+

It will be throw error, dosen't work

Results Content Log Received:

[Item][error]-Could not transform item into lava_bucket, it is invalid