How to get each playlist page from Spotify API in nodejs

I am trying to get all custom playlists from spotify API and put them in a picklist. I can only access 20 playlists at a time, so I created a while loop that uses the next-page property to loop through each page of the playlists, but for some reason it ends up in an infinite loop. I am guessing that the problem is in the uri = playlist.next line as shown below. Any help would be really appreciated, here's the code:

        //Request the user information...
        $.ajax({
            url: 'https://api.spotify.com/v1/me',
            headers: {
              'Authorization': 'Bearer ' + access_token
            },
            //... Create a list of the user playlists
            success: function(user) {
              var playlistURL = 'https://api.spotify.com/v1/users/' + user.id + '/playlists';

              appendPlaylists(playlistURL);

              function appendPlaylists(nextURL) {
                if (nextURL == null) {
                  return;
                }
                //Append playlists to the menu
                $.ajax({
                    url: nextURL,
                    headers: {
                      'Authorization': 'Bearer ' + access_token
                    },
                    success: function(playlists) {
                      console.log(nextURL);

                      var i = 0;
                      while (playlists.items[i] != null) {
                        console.log(playlists.items[i].name);
                        $('.all-playlists').append('<option value="' + playlists.items[i].href + '">' + playlists.items[i].name + '</option>')
                        i++;
                      }
                      appendPlaylists(playlists.next);
                    }    
                });
              }

              //Load the logged in div.
              $('#login').hide();
              $('#loggedin').show();
            }
        });