Retrieves the delayed future provided to [ctor@Dex.
Delayed.new].
This function can only return a [class@Dex.Future] before [method@Dex.Delayed.release] is called. After that, the delayed future is released and this function will return null.
| this |
a [class@Dex.Delayed] |
|
a [class@Dex.Future] or null |