code: function addCounts(o1, o2) {
    var result;
    if (o1 && o2) {
      result = _.merge(o1, o2, function (a, b) {
        return a + b;
      });
    }
    else if (o1) {
      result = o1;
    }
    else {
      result = o2;
    }
    return result;
  }
docs: given two objects that have the same keys and whose values are all integers return a new object that sums them together. If either object is null, return the other one.