@Udf
  public String chr(@UdfParameter(
      description = "Decimal codepoint") final Integer decimalCode) {
    if (decimalCode == null) {
      return null;
    }
    if (!Character.isValidCodePoint(decimalCode)) {
      return null;
    }
    final char[] resultChars = Character.toChars(decimalCode);
    return String.valueOf(resultChars);
  }
@Test
  public void shouldReturnNullForNullStringInput() {
    final String result = udf.chr((String) null);
    assertThat(result, is(nullValue()));
  }