code: @Nullable
    @OverrideOnDemand
    protected IUser getUserOfLoginName (@Nullable final String sLoginName)
    {
      return PhotonSecurityManager.getUserMgr ().getUserOfLoginName (sLoginName);
    }
docs: Get the {@link IUser} instance of the specified login name.
  
  @param sLoginName
  The login name to use. May be <code>null</code>.
  @return <code>null</code> if no such user exists.