code: public User getUser(String userName) {
          User result = null;
          for (User item : getUsersList()) {
              if (item.getName().equals(userName)) {
                  result = item;
              }
          }
          return result;
      }
docs: Get the particular User instance if the user
  can be found. Null otherwise.
  @param userName The name for which we search
  in the list of users.
  @return The instance of the particular user
  or null otherwise.