code: function createId (coll) {
    var _ = this
    var idProperty = _.__id()
    if (_.isEmpty(coll)) {
      return 1
    } else {
      var id = _.maxBy(coll, function (doc) {
        return doc[idProperty]
      })[idProperty]
  
      if (_.isFinite(id)) {
        // Increment integer id
        return ++id
      } else {
        // Generate string id
        return uuid()
      }
    }
  }
docs: Return incremented id or uuid Used to override underscore-db's createId with utils.createId