mapAsyncForUndefinable

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

U must not be Undefinable<*>.
- If you'd like return Undefinable<*> as U, use andThen().
- If the result of transformer is undefined, this throw an Error.

function mapAsyncForUndefinable<T, U>(input: Undefinable<T>, transformer: AsyncTransformFn<T, NotUndefined>): Promise<Undefinable>;

mapAsyncForUndefinable<T, U>(input: Undefinable<T>, transformer: AsyncTransformFn<T, NotUndefined>): Promise<Undefinable>

transformer: AsyncTransformFn<T, NotUndefined>

Promise<Undefinable>