One more question, how to return a list of x. For instance,

fun Route.genderRoutes() {
    val p = Program()
    get("/genders") { call.respond(p.run()) }
}

the function

p.run()

returns a list of users. Calling the api, I've got:

java.lang.StackOverflowError: null
	at com.google.gson.stream.JsonWriter.value(JsonWriter.java:522)