storage -> item data modifier not working

[
    {
      "function": "minecraft:copy_custom_data",
      "source": {
        "type": "minecraft:storage",
        "source": "hexenwerk:temp"
      },
      "ops": [
        {
          "source": "uuid",
          "target": "hexenwerk.uuid",
          "op": "merge"
        }
      ]
    }
  ]

i am using this modifier to copy data from a storage to an item
the contents of hexenwerk:temp look like this:
{uuid:23423}
when i now modify any item with the modifier its data gets changed to {components:{"minecraft:custom_data":{hexenwerk:{uuid:{}}}}} instead of actually inserting the value