code: function(keys) {
          requires(keys, 'undefined is not a valid key');
          _(arguments).forEach(keys => {
            this._include = this._include.concat(ensureArray(keys));
          });
          return this;
        }
docs: Include nested AV.Objects for the provided key.  You can use dot
  notation to specify which fields in the included object are also fetch.
  @param {String[]} keys The name of the key to include.
  @return {AV.Query} Returns the query, so you can chain this call.