mongoose types useTimestamps plugin w/ if block removed

useTimestamps.js

var mongoose = require('mongoose')
  , ObjectID = mongoose.ObjectID
  , BinaryParser = mongoose.mongo.BinaryParser;

exports.useTimestamps = function (schema, options) {
  schema.add({
      createdAt: Date
    , updatedAt: Date
  });
  schema.pre('save', function (next) {
    if (!this.createdAt) {
      this.createdAt = this.updatedAt = new Date;
    } else {
      this.updatedAt = new Date;
    }
    next();
  });
};