@SuppressWarnings("unchecked")
    public B clearMixins() {
        if (mixins != null) {
            // Avoid concurrent modification.
            List<ShapeId> mixinIds = new ArrayList<>(mixins.keySet());
            for (ShapeId id : mixinIds) {
                removeMixin(id);
            }
        }
        return (B) this;
    }
Removes all mixins.

@return Returns the builder.
smithy-model/src/main/java/software/amazon/smithy/model/shapes/AbstractShapeBuilder.java