CompletableDeferred builder with nullable generic parameter can be misused

[vsalavatov]

Consider a code like this:

interface T

object BadT : T
class GoodT : T

fun CoroutineScope.doStuff(flag: Boolean): Deferred<T> {
  if (!flag) return CompletableDeferred(BadT)
  return async { computeGoodT() }
}

after some thinking I decided to drop BadT and use nullability instead, so I naturally changed the code to

interface T

class GoodT : T

fun CoroutineScope.doStuff(flag: Boolean): Deferred<T?> {
  if (!flag) return CompletableDeferred(null)
  return async { computeGoodT() }
}

And was puzzled to see my tests stuck. During an investigation I noticed that after my change the CompletableDeferred started to resolve to public fun <T> CompletableDeferred(parent: Job? = null) instead of public fun <T> CompletableDeferred(value: T). I believe this misuse might occasionally happen, so an inspection would be nice

[vsalavatov]

Or maybe it would make more sense to make parent argument always explicit and non-null 🤔