You may need to convert a Stream emitting Optional to a Stream of values, emitting only values from existing Optional. (ie: without null value and not dealing with Optional.empty()).

Optional<String> op1 = Optional.empty();
Optional<String> op2 = Optional.of("Hello World");

List<String> result = Stream.of(op1, op2)
                            .filter(Optional::isPresent)
                            .map(Optional::get)
                            .collect(Collectors.toList());

System.out.println(result); //[Hello World]