@Override
    @SuppressWarnings("unchecked")
    public Set<Shape> select(Model model, StartingContext context) {
        Collection<? extends Shape> startingShapes = context.getStartingShapes();
        if (startingShapes == null) {
            return model.toSet();
        } else if (startingShapes instanceof Set) {
            return (Set<Shape>) startingShapes;
        } else {
            return new HashSet<>(startingShapes);
        }
    }
An optimized Selector implementation that uses the provided Model directly
rather than needing to send each shape through the Selector machinery.

@see Selector#IDENTITY
smithy-model/src/main/java/software/amazon/smithy/model/selector/IdentitySelector.java