public Optional<ArnTrait> getEffectiveOperationArn(ToShapeId service, ToShapeId operation) {
        return Optional.ofNullable(effectiveArns.get(service.toShapeId()))
                .flatMap(operationArns -> Optional.ofNullable(operationArns.get(operation.toShapeId())));
    }
Gets the effective ARN of an operation based on the identifier bindings
of the operation bound to a resource contained within a service.

<p>An operation bound to a resource using a collection binding has an
effective ARN of the parent of the resource. An operation bound to a
resource using an instance binding uses the ARN of the resource as
its effective ARN.

@param service Service the operation is bound within.
@param operation Operation shape for which to find the effective ARN.
@return Returns the optionally found effective ARN.
smithy-aws-traits/src/main/java/software/amazon/smithy/aws/traits/ArnIndex.java