public static Instant parseDateTime(String s) throws DateTimeParseException {
    ValidationUtils.checkArgument(Objects.nonNull(s), "Input String cannot be null.");
    try {
      return Instant.ofEpochMilli(Long.parseLong(s));
    } catch (NumberFormatException e) {
      return Instant.parse(s);
    }
  }
@Test
  public void testParseDateTimeWithNull() {
    assertThrows(IllegalArgumentException.class, () -> {
      DateTimeUtils.parseDateTime(null);
    });
  }