public Optional<Shape> getPayloadShape() {
        return Optional.ofNullable(payloadShape);
    }
Gets the payload shape of the topic.

<p>The payload shape is either a structure for a single-event
event stream, or a union for a multi-event event stream.

@return Returns the optional payload target.
smithy-mqtt-traits/src/main/java/software/amazon/smithy/mqtt/traits/TopicBinding.java