Object reference not set to an instance of the object

Hello Ramco,

You need to check null refernce for channelsListResponse before accessing items property, you are trying to access from of null response that the reason you are getting this error,

var yt = new YouTubeService(new BaseClientService.Initializer() { ApiKey = "AIzaSyAu9f5blF7idzt6cG2l29vQ9g4HBdYy36H" });
                var channelsListRequest = yt.Channels.List("contentDetails");
                channelsListRequest.ForUsername = "g3ZrkCBQ3GngW-m_nKoaSw";
                var channelsListResponse = channelsListRequest.Execute();
                int VideoCount = 1;
                if(channelsListResponse != null)
                {
                foreach (var channel in channelsListResponse.Items)
                {
                    var uploadsListId = channel.ContentDetails.RelatedPlaylists.Uploads;
                    var nextPageToken = "";
                    while (nextPageToken != null)
                    {
                        var playlistItemsListRequest = yt.PlaylistItems.List("snippet");
                        playlistItemsListRequest.PlaylistId = uploadsListId;
                        playlistItemsListRequest.MaxResults = 50;
                        playlistItemsListRequest.PageToken = nextPageToken;

                        var playlistItemsListResponse = playlistItemsListRequest.Execute();
                        foreach (var playlistItem in playlistItemsListResponse.Items)
                        {
                            Console.WriteLine("Sl No={0}", VideoCount);
                            Console.Write("Video ID ={0} ", "youtube.com/embed/" + playlistItem.Snippet.ResourceId.VideoId);

                            VideoCount++;
                        }
                        nextPageToken = playlistItemsListResponse.NextPageToken;
                    }
                    Console.ReadLine();
                }
               }