code: function(attr, amount) {
        if (_.isUndefined(amount) || _.isNull(amount)) {
          amount = 1;
        }
        return this.set(attr, new Parse.Op.Increment(amount));
      }
docs: Atomically increments the value of the given attribute the next time the
  object is saved. If no amount is specified, 1 is used by default.
  
  @param attr {String} The key.
  @param amount {Number} The amount to increment by.