mapOrElseAsyncForNullable

Return the result of transformer with using input as an argument for it if input is not null. Otherwise, return the result of recoverer.

Basically, this operation is a combination mapAsync() and unwrapOrElseAsync().

• U must not be Nullable<*>.
  • If the result of transformer is null, this throw an Error.
  • If the result of recoverer is null, this throw an Error`.
• If you'd like to accept Nullable<*> as U, use a combination andThenAsync() and orElseAsync().