Requesting multiple Youtube playlist ids in a foreach

// GlobalVariables.YoutubePlaylistId is defined like this:
//                        public static string[] YoutubePlaylistId = {"---A-PLAYLIST-ID---", "---ANOTHER-PLAYLIST-ID---"};

#region "Load Youtube Data"
            int i = 0;
            foreach (string playlistID in GlobalVariables.YoutubePlaylistId)
            {
                RestRequest YoutubeRequest = new RestRequest("/playlistItems?part=snippet&playlistId=" + playlistID + "&key=" + GlobalVariables.YoutubeClientID + "&maxResults=25", Method.GET);
                YoutubeRequest.RequestFormat = DataFormat.Json;
                GlobalVariables.YoutubeClient.ExecuteAsync<PlaylistObject>(YoutubeRequest, (YoutubeResponse) =>
                {
                    PlaylistObject pl = YoutubeResponse.Data;
                    NextPageToken[i] = pl.nextPageToken;
                    foreach (Item v in pl.items)
                    {
                        if (v.snippet.title != "Private video")
                        {
                            AddVideo(v.snippet, i);
                        }
                    }
                    i++;
                });
            }

// This gives me a Object reference not set to an instance of an object. Have tried to find which object/line of code. Using RestSharp and RestSharpEx