Ember js build throws null coalescing error

I'm following the guide here to create getters in my component. However following the guide as it is gives me an error

Support for the experimental syntax 'nullishCoalescingOperator' isn't currently enabled

Searching through the guides, I couldn't find any documentation on how to enable this. I've tried this in my ember-cli-build.js file but that didn't work

'ember-cli-babel': {
  includePolyfill: true,
  nullishCoalescingOperator: true
}

and

'ember-cli-babel': {
  includePolyfill: true,
  nullishCoalescingOperator: 'enabled'
}