public static String toCsv(List<String> src) {
        // return src == null ? null : String.join(", ", src.toArray(new String[0]));
        return join(src, ", ");
    }
@Test
    public void testToCsv() {
        assertEquals(toCsv(Collections.<String>emptyList()), (""));
        assertEquals(toCsv(Collections.singletonList("a")), ("a"));
        assertEquals(toCsv(Arrays.asList("a", "b", "c")), ("a, b, c"));
    }