Find an asset by key
        E.g.
            shopify.Asset.find('layout/theme.liquid', theme_id=99)

def find(cls, key=None, **kwargs):
        """
        Find an asset by key
        E.g.
            shopify.Asset.find('layout/theme.liquid', theme_id=99)
        """
        if not key:
            return super(Asset, cls).find(**kwargs)

        params = {"asset[key]": key}
        params.update(kwargs)
        theme_id = params.get("theme_id")
        path_prefix = "%s/themes/%s" % (cls.site, theme_id) if theme_id else cls.site

        resource = cls.find_one("%s/assets.%s" % (path_prefix, cls.format.extension), **params)

        if theme_id and resource:
            resource._prefix_options["theme_id"] = theme_id
        return resource