How to generate multivalue map with random values and inject into request body using a feeder in Gatling - scala

Question

I'm writing a load test for an api and want to create a feeder which generates random values to inject into the body of the POST request. I initially tried copying the random email example from the documentation and adding additional fields to the generated map, but when that didn't work I went down to a single field, basically copying the documentation; however, even this doesn't work for some reason. There are a bunch of solutions on here that use this syntax as well, but something about the way I'm doing is causing the fields I try to inject into the body to be null when the request is made.
Current Code:
val userFeeder: Iterator[Map[String, Unit]] =
Iterator.continually(Map("userName" -> ("user_" + Random.alphanumeric.take(15).mkString)))
var scn: ScenarioBuilder = scenario("GENERATE USER")
.feed(userFeeder)
.exec(
http("CREATE USER")
.post(userBaseUrl)
.headers(userHeaders)
.body(StringBody("userName: ${userName}")))
setUp(
scn.inject(atOnceUsers(1))
)
Ideally I'd like to be able to expand the feeder to include multiple values, i.e.
val userFeeder: Iterator[Map[String, Unit]] =
Iterator.continually(Map("userName" -> ("user_" + Random.alphanumeric.take(15).mkString),
"userEmail" -> (Random.alphanumeric.take(15).mkString) + "#random.edu"),
"address" -> Random.alphanumeric.take(15).mkString)))
and so on, but I'm a little stumped as to why my current code doesn't even work, as it seems to follow the documentation example pretty faithfully. The values are always null in my requests despite trying a few different strategies.
Log output
body:StringChunksRequestBody{contentType='application/json', charset=UTF-8, content=userName: ()}

Answer 1

Figured it out. Turns out that even though Feeder is a wrapper for Iterator, the proper way to do what I want is to declare it like this:
val userFeeder: Feeder[Any] =
Iterator.continually(Map("userName" -> ("user_" + Random.alphanumeric.take(15).mkString),
"userEmail" -> (Random.alphanumeric.take(15).mkString) + "#random.edu"),
"address" -> Random.alphanumeric.take(15).mkString)))