public static <T> String join(final String... elements) {
    return join(elements, EMPTY_STRING);
  }
@Test
  public void testStringJoinWithJavaImpl() {
    assertNull(StringUtils.join(",", null));
    assertEquals("", String.join(",", Collections.singletonList("")));
    assertEquals(",", String.join(",", Arrays.asList("", "")));
    assertEquals("a,", String.join(",", Arrays.asList("a", "")));
  }