public List <string> getSubForums(string forumName, string requestingUser)
        {
            List <string> input = new List <string>()
            {
                forumName, requestingUser
            };

            if (Constants.isValidInput(input))
            {
                lock (o)
                {
                    // get user permissions and verify can get a list of sub forums
                    return(_fm.getSubForums(forumName));
                }
            }
            return(null);
        }