// Code-Platzhalter
        private async Task<(bool success, int lastPosition, MongoVirtualFolder folder)> WalkPath(string[] pathParts, VirtualFolder startFolder = null)
        {
            var folder = await ToMongoVirtualFolder(startFolder) ?? _rootFolder;            for (var i = 0; i < pathParts.Length; i++)
            {
                var part = pathParts[i];
// 
// The error occurs here:
//
                var newFolder = await Collection
                    .Where(x => x.Parent == folder.Id && x.Name == part)
                    .FirstOrDefaultAsync()
                    .ConfigureAwait(false);
                if (newFolder == null)
                {
                    return (false, i, folder);
                }                folder = newFolder;
            }
            return (true, pathParts.Length, folder);
        }        public Task<VirtualFolder> CreateFolder(string path, VirtualFolder startFolder = null)
        {
            var folderParts = path.Split(new char[] { '\\', '/' }, StringSplitOptions.RemoveEmptyEntries);
            return CreateFolder(folderParts, startFolder);
        }        public async Task<VirtualFolder> CreateFolder(string[] folderParts, VirtualFolder startFolder = null)
        {
            var (success, i, folder) = await WalkPath(folderParts, startFolder);
            if (!success)
            {
                int j = i;
                try
                {
                    for (j = i; j < folderParts.Length; j++)
                    {
                        var newFolder = new MongoVirtualFolder
                        {
                            Name = folderParts[j],
                            Parent = folder.Id,
                        };                        await Collection.InsertOneAsync(newFolder);
                        folder = newFolder;
                    }
                }
                catch (MongoWriteException exception) when (exception.InnerException is MongoBulkWriteException InnerException)
                {
                    if (InnerException.WriteErrors.Any(x => x.Category == ServerErrorCategory.DuplicateKey))
                    {
                        //Duplicate key
                        var searchArray = folderParts.AsEnumerable().Skip(i).Take(folderParts.Length - i).ToArray();
                        Console.WriteLine($"Concurrency warning! Retrying ({string.Join("/", folderParts)})");
                        return await CreateFolder(searchArray, folder);
                    }                    throw;
                }
                catch (Exception e)
                {
                    Console.WriteLine(e);
                    throw;
                }                folder.Folders = new List<VirtualFolderSlim>();
                folder.VirtualFiles = new List<VirtualFile>();
            }
            else
            {
                await LoadFolderContents(folder);
            }            return folder;
        }

// Entrypoint:
async Task<Dictionary<string, (DirectoryInfo, VirtualFolder)>> CreateFolders1(VirtualFolder fold, DirectoryInfo dir)
            {
                var result = new Dictionary<string, (DirectoryInfo, VirtualFolder)>();
                var dirs = dir.EnumerateDirectories("*", SearchOption.TopDirectoryOnly);                //var subFolders = await dirs.Select(x => _virtualFolderDal.CreateFolder(x.Name, fold)).WhenAll();                var subFolders = await dirs.Select(x => ___CreateFolder(fold, x)).WhenAll();
                foreach (var virtualFolder in subFolders.SelectMany(x => x))
                {
                    result[virtualFolder.Key] = virtualFolder.Value;
                }                return result;                async Task<Dictionary<string, (DirectoryInfo, VirtualFolder)>> ___CreateFolder(VirtualFolder __fold, DirectoryInfo __dir)
                {
                    var subFolder = await _virtualFolderDal.CreateFolder(__dir.Name, __fold);
                    return await CreateFolders1(subFolder, __dir);
                }
            }