    @Test
    void testFilterToReferenceMap() {

        Map<String, String> map = new HashMap<>();
        map.put("ok", "cool");
        map.put("derklaro", "cool");
        map.put("reformcloud", "good");

        ReferencedOptional<String> optional = Streams.filterToReference(map, t -> t.equals("ok"));
        Assertions.assertTrue(optional.isPresent());
        Assertions.assertEquals("cool", optional.get());
    }