code: @Nullable
    public IUser getUserOfLoginName (@Nullable final String sLoginName)
    {
      if (StringHelper.hasNoText (sLoginName))
        return null;
  
      return findFirst (x -> x.getLoginName ().equals (sLoginName));
    }
docs: Get the user with the specified login name
  
  @param sLoginName
  The login name to be checked. May be <code>null</code>.
  @return <code>null</code> if no such user exists