storage -> item data modifier not working

json [ { "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