code: function normalizeEntity(base, input) {
    if (!input) return {};
  
    var result = Object.assign(clone(input), {
      class: normalizeClass(input.class),
      properties: normalizeProperties(input.properties),
      entities: normalizeEntities(base, input.entities),
      links: normalizeLinks(base, input.links),
      actions: normalizeActions(base, input.actions),
      title: input.title
    });
  
    // strip undefined values from the result
    return filter(result, function (v) {
      return typeof v !== 'undefined';
    });
  }
docs: Takes the `input` entity object and normalizes it into a valid siren object.
  
  @param {String} base   The base URL for this API.
  @param {Object} input  The entity object to normalize.
  @return {Object}