`RandomNumberViewModel` `replaceError` attempt.

random_number_view_model_replace_error.swift

final class RandomNumberViewModel: ObservableObject {

	/* … */

	init() {
		randomNumberPing
			.map {
				randomNumberPublisher()
					.map(Optional.some) /// (1) Boxing values into an `Optional`.
					.replaceError(with: nil) /// (2) Swapping out errors with `nil`s.
			}
			.switchToLatest()
			.print()
			.receive(on: DispatchQueue.main)
			.assign(to: \.randomNumber, onWeak: self)
			.store(in: &subscriptions)
	}
}