code: @Nullable
    public LoginInfo getLoginInfo (@Nullable final String sUserID)
    {
      return m_aRWLock.readLocked ( () -> m_aLoggedInUsers.get (sUserID));
    }
docs: Get the login details of the specified user.
  
  @param sUserID
  The user ID to check. May be <code>null</code>.
  @return <code>null</code> if the passed user is not logged in.