Kapacitor - Stream node fields to alert message

Hey, trying to get two field values out of a stream node. one’s an integer and the other a string. What I have does not work despite chronograf suggesting the syntax it’s valid.

var data = stream
    |eval(lambda: "field.4") //string
    |eval(lambda: "field.8") //int

Then construct an alert message from that

var message = '{{ index .Fields "identifier" }} {{ index .Tags "host" }} {{ .TaskName }} is {{.Level}} value: {{ index .Fields "value" }}'

However, when I trigger a test alert, I get a “no value” where I’d expect to see the value of “field.4” the rest of the message is working as expected.
Any help appreciated. Thanks.