@Udf
  public String extractHost(
      @UdfParameter(description = "a valid URL") final String input) {
    return UrlParser.extract(input, URI::getHost);
  }
@Test
  public void shouldReturnNullIfNoHost() {
    assertThat(extractUdf.extractHost("https:///current/ksql/docs/syntax-reference.html#scalar-functions"), nullValue());
  }