code: function(userId, options, callback) {
      var path;
      if (typeof userId === 'string') {
        path = '/v1/users/' + encodeURIComponent(userId) + '/playlists';
      } else if (typeof userId === 'object') {
        callback = options;
        options = userId;
        path = '/v1/me/playlists';
      } /* undefined */ else {
        path = '/v1/me/playlists';
      }
  
      return WebApiRequest.builder(this.getAccessToken())
        .withPath(path)
        .withQueryParameters(options)
        .build()
        .execute(HttpManager.get, callback);
    }
docs: Get a user's playlists.
  @param {string} userId An optional id of the user. If you know the Spotify URI it is easy
  to find the id (e.g. spotify:user:<here_is_the_id>). If not provided, the id of the user that granted
  the permissions will be used.
  @param {Object} [options] The options supplied to this request.
  @param {requestCallback} [callback] Optional callback method to be called instead of the promise.
  @example getUserPlaylists('thelinmichael').then(...)
  @returns {Promise|undefined} A promise that if successful, resolves to an object containing
  a list of playlists. If rejected, it contains an error object. Not returned if a callback is given.