vs code transform error

[tofulm]

this snippet is OK

	"aa": {
		"prefix": "aa",
		"body": "$1 (${1/(.*)/${1:/upcase}/}) $0"
	},

=> john (JOHN)

But :

	"bb": {
		"prefix": "bb",
		"body": "(${1/(.*)/${1:/upcase}/}) $0"
	},

=> (john)

why is it mandatory to have $1 for the transformation to work

In vscodium, it works