KafkaTableSourceSinkFactoryBase#getFlinkKafkaPartitioner does not compile with Java 9

private Optional<FlinkKafkaPartitioner<Row>> getFlinkKafkaPartitioner(DescriptorProperties descriptorProperties) {
	return descriptorProperties
		.getOptionalString(CONNECTOR_SINK_PARTITIONER)
		.flatMap((String partitionerString) -> {
			switch (partitionerString) {
				case CONNECTOR_SINK_PARTITIONER_VALUE_FIXED:
					return Optional.of(new FlinkFixedPartitioner<>());
				case CONNECTOR_SINK_PARTITIONER_VALUE_ROUND_ROBIN:
					return Optional.empty();
				case CONNECTOR_SINK_PARTITIONER_VALUE_CUSTOM:
					final Class<? extends FlinkKafkaPartitioner> partitionerClass =
						descriptorProperties.getClass(CONNECTOR_SINK_PARTITIONER_CLASS, FlinkKafkaPartitioner.class);
					return Optional.of(InstantiationUtil.instantiate(partitionerClass));
				default:
					throw new TableException("Unsupported sink partitioner. Validator should have checked that.");
			}
		});
}