public Optional<ShapeId> getOptionalError() {
        return Optional.ofNullable(error);
    }
The error shape which indicates to a client that an endpoint they are
using is no longer valid.

<p>This error MUST be bound to every operation bound to the service
which is marked with an {@link ClientDiscoveredEndpointTrait}.</p>

@return The ShapeId of the invalid endpoint error.
smithy-aws-traits/src/main/java/software/amazon/smithy/aws/traits/clientendpointdiscovery/ClientEndpointDiscoveryTrait.java