Completion Exception Or Null
abstract fun getCompletionExceptionOrNull(): Throwable?(source)
Returns completion exception result if this deferred was cancelled and has completed,
null if it had completed normally, or throws IllegalStateException if this deferred value has not completed yet.
This function is designed to be used from invokeOnCompletion handlers, when there is an absolute certainty that the value is already complete. See also getCompleted.
Note: This is an experimental api. This function may be removed or renamed in the future.