code: @Override
      public List<User> searchUsers(String search) throws AuthenticationException {
          // Complete list of users
          String[] users = file_store.keySet().toArray(
                  new String[file_store.size()]);
          List<User> found = new ArrayList<User>();
  
          // Look through the list for anyone who matches
          for (int i = 0; i < users.length; i++) {
              if (users[i].toLowerCase().contains(search.toLowerCase())) {
                  found.add(getUser(users[i]));
              }
          }
  
          // Return the list
          return found;
      }
docs: Returns a list of users matching the search.
  
  @param search The search string to execute.
  @return A list of usernames (String) that match the search.
  @throws AuthenticationException if there was an error searching.