@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 shouldThrowExceptionForExamplesOfUnsupportedElementTypes() {
    assertThrows(KsqlFunctionException.class,
        () -> arrayJoinUDF.join(Arrays.asList('a','b')));
    assertThrows(KsqlFunctionException.class,
        () -> arrayJoinUDF.join(Arrays.asList(BigInteger.ONE,BigInteger.ZERO)));
    assertThrows(KsqlFunctionException.class,
        () -> arrayJoinUDF.join(Arrays.asList(-23.0f,42.42f,0.0f)));
    assertThrows(KsqlFunctionException.class,
        () -> arrayJoinUDF.join(Arrays.asList(
            new HashSet<>(Arrays.asList("foo", "blah")),
            new HashSet<>(Arrays.asList("ksqlDB", "UDF"))
        ))
    );
  }