public Task <ApplicationUser> FindByIdAsync(string userId, CancellationToken cancellationToken = default(CancellationToken)) { cancellationToken.ThrowIfCancellationRequested(); var isValidGuid = Guid.TryParse(userId, out var userGuid); if (!isValidGuid) { return(Task.FromResult <ApplicationUser>(null)); } return(_usersTable.FindByIdAsync(userGuid)); }