@Udf
  public Integer len(
      @UdfParameter(description = "The input string") final String input) {
    if (input == null) {
      return null;
    }
    return input.length();
  }
@Test
  public void shouldReturnNullForNullInput() {
    assertThat(udf.len((String) null), is(nullValue()));
    assertThat(udf.len((ByteBuffer) null), is(nullValue()));
  }