/* Except starting at line 718 */

// If a duplicate is found, prevent it from being added and
// optionally merge it into the existing model.
if (existing = this.get(id)) {
  if (remove) modelMap[existing.cid] = true;
  if (merge) {
    attrs = attrs === model ? model.attributes : attrs;
    if (options.parse) attrs = existing.parse(attrs, options);
    existing.set(attrs, options);
    if (sortable && !sort && existing.hasChanged(sortAttr)) sort = true;
  }
  models[i] = existing;