public void AcceptUserFriend(User u, int?friend_id)
 {
     using (SqlConnection connection = new SqlConnection(connectionString))
     {
         SqlCommand command = new SqlCommand(UserQueries.AcceptUserFriend(u, friend_id), connection);
         connection.Open();
         try
         {
             command.ExecuteNonQuery();
         }
         catch (SqlException e)
         {
             throw e;
         }
     }
 }