code: function (object, options, callback) {
          var version;
  
          if (!options || !(version = semver.valid(options.normalizeVersion, true)) || !normalizers[version]) {
              return callback(new Error('Version not specified or invalid: ' + options.normalizeVersion));
          }
  
          return normalizers[version].normalizeSingle(object, options, callback);
      }
docs: Normalizes a single request or item as per the provided version.
  
  @param {Object} object - The entity to be normalized.
  @param {Object} options - The set of options to be applied to the current normalization.
  @param {String} options.normalizeVersion - The base collection schema version for which to normalize.
  @param {?Boolean} [options.mutate=false] - When set to true, normalization is done in place.
  @param {?Boolean} [options.noDefaults=false] - When set to true, sensible defaults are not added.
  @param {?Boolean} [options.prioritizeV2=false] - When set to true, v2 style properties are checked first.
  @param {?Boolean} [options.retainEmptyValues=false] - When set to true, empty values are set to '' instead of
  being removed.
  @param {Function} callback - The function invoked when the normalization has completed.