Объект в футляре или Optional в Java 8 и Java 9. Часть 4: «Как футляром с двойным дном закрыть дыру в Java“

import java.util.Optional;
import java.util.function.BiFunction;
import java.util.function.Consumer;
import java.util.stream.Stream;

/**
 * Объект-контейнер, который может содержать один из двух типов объектов.
 */
class Union<T1, T2> {
    private final Optional<T1> first;
    private final Optional<T2> second;

    Union(T1 first, T2 second) {

        assert (first == null && second != null) || (first != null && second == null);

        this.first = Optional.ofNullable(first);
        this.second = Optional.ofNullable(second);
    }

    public boolean isFirstPresent() {
        return first.isPresent();
    }

    public boolean isSecondPresent() {
        return second.isPresent();
    }

    public <U> Stream<U> map(BiFunction<T1, T2, U> function) {
        return Stream.of(function.apply(first.orElse(null), second.orElse(null)));
    }

    public void forEach(Consumer<? super T1> whenValue1, Consumer<? super T2> whenValue2) {
        first.ifPresent(whenValue1);
        second.ifPresent(whenValue2);
    }
} 

final class SuccessOrFailure extends Union<String, BatchExceptions> {

    private SuccessOrFailure(final String batchName, final BatchExceptions someException) {
        super(batchName, someException);
    }

    public static SuccessOrFailure createFromSuccess(final String batchName) {
        return new SuccessOrFailure(batchName, null);
    }

    public static SuccessOrFailure createFromFailure(final BatchExceptions someExceptions) {
        return new SuccessOrFailure(null, someExceptions);
    }
}