Function usage question to have specific field based on arugment.

[buzzerpuzzle]

Hi team!

I'm thinking about whether I could use parameter to determine whether to have specific field.

Base on my last question, I could pass test argument to determine whether to have b field.

testFunction.dhall
let testFunction = \(args : { test : Bool }) ->
  { a = "123", b = if args.test then Some "test" else None Text }
in testFunction

I would like to make it to be more flexible more than just text but got the issue with mismatch field error.
Hope you guys could give me more context how to make it work.

a.dhall

let a = {
    version = "123",
    description = "456"
} in a

b.dhall

let testFunction = \(args : { test : Bool }) ->
  { a = "123", b = if args.test then ./a.dhall else None Text }
in testFunction

Error message

dhall-to-yaml-ng <<< './b.dhall {test=True}'


↳ ./b.dhall

Error: ❰if❱ branches must have matching types

- None
+ Optional
…

2│                    if args.test then ./a.dhall else None Text

/Users/Projects/learning-dhall/b.dhall:2:20

1│ ./b.dhall

(input):1:1

Thanks!