Using default values to skip array value

This post is inspired by the following one on stackoverflow: amazon web services - Use stage parameters to skip fields in Serverless Framework - Stack Overflow

In the code below, is there a particular 'default value' that could be set as to skip the array value? I would like DevKey1 and DevKey2 for the dev stage and only ProdKey1 for the v1 stage.

frameworkVersion: '3'

    name: 'dev'
    keyName1: DevKey1
    keyName2: DevKey2
    name: 'v1'
    keyName1: ProdKey1

  name: aws
      - ${param:keyName1}
      - ${param:keyName2, 'defult value'}

I vaguely remember that they aren’t quite possible with the lazy class loading and method binding. Essentially the bytecode needs to know the exact signature of the method you call and that messes this up somehow. Kodi nox