@Override
    public String convertTo(SortedSet<Path> value) {
        if (value == null) {
            throw new ParameterException("String list of Paths must not be null.");
        }

        return value.stream().map(Path::toString).collect(Collectors.joining(","));
    }
@Test(expected = ParameterException.class)
    public void testConvertToNull() {
        converter.convertTo(null);
    }