@Udf
  public <T> String join(
      @UdfParameter(description = "the array to join using the default delimiter '"
          + DEFAULT_DELIMITER + "'") final List<T> array
  ) {
    return join(array, DEFAULT_DELIMITER);
  }
@Test
  public void shouldReturnNullForNullInput() {
    assertThat(arrayJoinUDF.join(null), nullValue());
    assertThat(arrayJoinUDF.join(null,CUSTOM_DELIMITER), nullValue());
  }