code: public static BaasUser withUserName(String username) {
          BaasUser current = current();
          if (current != null && current.username.equals(username)) {
              return current;
          }
          return new BaasUser(username);
      }
docs: Creates a new user bound to username.
  If the provided username is the same one of the currently logged in account
  the same instance of {@link #current()} is returned.
  
  @param username a non empty username
  @return a <code>BaasUser</code>