public List <Wallet> GetWalletsByUser(User user) { if (user == null) { throw new ArgumentNullException("user"); } User loggedUser = userSession.GetLoggedUser(); if (loggedUser != null) { if (user.IsFriend(loggedUser)) { return(walletProvider.FindWalletsByUser(user)); } return(new List <Wallet>()); } else { throw new UserNotLoggedInException(); } }