code: function(key, value) {
          var data = {},
              keys,
              first,
              subkey;
          if (key.indexOf(".") > -1) {
              keys = key.split(".");
              first = keys.shift();
              subkey = keys.join(".");
              data[first] = this._set_create_object(subkey, value);
          } else {
              data[key] = value;
          }
          return data;
      }
docs: If you are setting a key of 'foo.bar' or 'bar', this creates
  the appropriate object for you to recursively merge with the
  current attributes.